After playing with Sikh recently, I was forced to conclude that my suspicion with it has been mostly accurate all along: aside from "save the burning world", if you want to even bother with that, converting to Sikh and staying there has virtually no upside.
Obvious:
Sikh's baseline bonuses are morale +5% and military tech cost -5%. While these are not strictly awful, they're the only reliably useful bonuses you get (the conversion resistance is generally not very important). Guru bonuses range from amazing (2% strength and -2 unrest) to lackluster (10% stabcost) to nothing (sometimes you don't have one), and are uncontrollable.
Hindu can save you more monarch points, is more stable on average due to +TTF and being more common initially, and even fights better if you pick up their 5% discipline deity (which is much stronger than 5% morale).
Hidden:
However, the above is the obvious disadvantage. What is the hidden disadvantage of Sikh? Vassals. While Sikh players can use a Hindu decision and "save the burning world" (requires inquisitor) to get to +5% strength from decisions, getting to a base 10% strength with religious, Sikh player vassals can't do so. They won't take the Hindu decision because they're not Hindu (excepting enforce religion, which can only be done on the few Hindus that take religious to be useful). I have played over 200 years feeding 8 different vassals and not a single one has taken the "save the burning world" decision, leading me to believe that even if the AI does take it, it's anything but reliable.
In essence, this means that feeding vassals to convert stuff to Sikh for you is roughly as useful as feeding vassals to convert stuff to animist for you. Feeding an Arabian ideas vassal primary culture Sunni provinces is no safe bet to get it all converted lol, though it at least helps a little because they'll chunk through the lower tax stuff that would still take you a while due to being hostile culture.
Of course, you could go the tolerance route...but Sikh gets nothing that helps it tolerate non-true faith. If you want to just tolerate everything, Hindu has both true faith and heretic tolerance and can get another one from decision (not that there will be much Sikh to tolerate anyway w/o player spreading it), so Hindus (especially former Sultanates with +3 heathen tolerance) can blithely conquer with humanist; Sikh gets no advantage in this regard either.
The sole exception that is practically useful to feed as Sikh (and animist) is Najd, which thankfully takes religious + administrative and despite taking no decisions to boost strength will still have 10% strength and 4 missionaries just because it's Najd.
You can of course conquer Rome for a 3rd missionary, though managing it before 1700ish is kind of difficult to do with any practicality.
Overall:
I'd like to see something that creates incentive to switch to Sikh. The vassals thing is probably just an oversight; I hadn't considered it myself but even Confucian/Hindu/Buddhist vassals at least take a 2% decision consistently, and that makes a big difference since it lets even former Sunni nations convert up to around 10 tax in primary/accepted cultures, and up to around 8 pretty quickly (there aren't a ton of provinces more than 8). More importantly, Sikh gets no reformation benefit, no actually weakening you compared to Hindu in terms of bonuses despite being harder to spread. I'm not sure what to do with it, but after using it heavily I can honestly say for the first time that I prefer Buddhist/Confucian to a non-pagan faith, simply because those faiths despite being bland got their conversion power buffed respectably (you can get 5% as Buddhist without switching for example) and have the option to go both a tolerance route or a conversion route, with the latter supplemented reasonably by vassals and rather powerful for nations like Lan Xang or the new Sukhotai who can run around with 11% constant conversion power of their own and 6 TTF.
Obvious:
Sikh's baseline bonuses are morale +5% and military tech cost -5%. While these are not strictly awful, they're the only reliably useful bonuses you get (the conversion resistance is generally not very important). Guru bonuses range from amazing (2% strength and -2 unrest) to lackluster (10% stabcost) to nothing (sometimes you don't have one), and are uncontrollable.
Hindu can save you more monarch points, is more stable on average due to +TTF and being more common initially, and even fights better if you pick up their 5% discipline deity (which is much stronger than 5% morale).
Hidden:
However, the above is the obvious disadvantage. What is the hidden disadvantage of Sikh? Vassals. While Sikh players can use a Hindu decision and "save the burning world" (requires inquisitor) to get to +5% strength from decisions, getting to a base 10% strength with religious, Sikh player vassals can't do so. They won't take the Hindu decision because they're not Hindu (excepting enforce religion, which can only be done on the few Hindus that take religious to be useful). I have played over 200 years feeding 8 different vassals and not a single one has taken the "save the burning world" decision, leading me to believe that even if the AI does take it, it's anything but reliable.
In essence, this means that feeding vassals to convert stuff to Sikh for you is roughly as useful as feeding vassals to convert stuff to animist for you. Feeding an Arabian ideas vassal primary culture Sunni provinces is no safe bet to get it all converted lol, though it at least helps a little because they'll chunk through the lower tax stuff that would still take you a while due to being hostile culture.
Of course, you could go the tolerance route...but Sikh gets nothing that helps it tolerate non-true faith. If you want to just tolerate everything, Hindu has both true faith and heretic tolerance and can get another one from decision (not that there will be much Sikh to tolerate anyway w/o player spreading it), so Hindus (especially former Sultanates with +3 heathen tolerance) can blithely conquer with humanist; Sikh gets no advantage in this regard either.
The sole exception that is practically useful to feed as Sikh (and animist) is Najd, which thankfully takes religious + administrative and despite taking no decisions to boost strength will still have 10% strength and 4 missionaries just because it's Najd.
You can of course conquer Rome for a 3rd missionary, though managing it before 1700ish is kind of difficult to do with any practicality.
Overall:
I'd like to see something that creates incentive to switch to Sikh. The vassals thing is probably just an oversight; I hadn't considered it myself but even Confucian/Hindu/Buddhist vassals at least take a 2% decision consistently, and that makes a big difference since it lets even former Sunni nations convert up to around 10 tax in primary/accepted cultures, and up to around 8 pretty quickly (there aren't a ton of provinces more than 8). More importantly, Sikh gets no reformation benefit, no actually weakening you compared to Hindu in terms of bonuses despite being harder to spread. I'm not sure what to do with it, but after using it heavily I can honestly say for the first time that I prefer Buddhist/Confucian to a non-pagan faith, simply because those faiths despite being bland got their conversion power buffed respectably (you can get 5% as Buddhist without switching for example) and have the option to go both a tolerance route or a conversion route, with the latter supplemented reasonably by vassals and rather powerful for nations like Lan Xang or the new Sukhotai who can run around with 11% constant conversion power of their own and 6 TTF.
