Ive played natives in EU3 and I think they are extremely playable. Just because it actually takes some time to annex the entirety of Europe does not mean it is unplayable - unless you are a bad player of course, but very easy difficulty can fix that.
Your condescension is noted.
You know how people complain about how truce timers make certain countries "unplayable", like Scotland, because they have only one "natural" route of expansion and waiting 15 years at speed 5 to do anything again is incredibly tedious?
Well, here's how an EUIII native plays:
1) Annex everything in the immediate vicinity.
2) Wait decades doing literally nothing.
3) Do some colonising once you can eventually grab the colonist idea. This will also likely be for a few decades, depending on which natives you are playing. You can do nothing else in the meantime. There are other possibilities for your one pre-European-contact idea besides colonising - in that case, add more decades doing literally nothing.
4) See which European shows up next to you. If it's Spain, good game, you can start over (fighting them is not generally feasible despite the AI's inability to support seaborne invasions since your armies will melt like butter against theirs and they will instantly seize any province they take, meaning you'd have to win it back in the peace and lol good luck with that because the AI is hardwired to think they can beat you regardless of the facts on the ground). If it's Portugal, hope that the RNG has given you a monarch that can Westernise (they'll also attack you but their armies are small enough to crush with overwhelming superiority). If no such ruler is in the offing, good game, you can start over. If neither of them shows up in 150 years, good game, you can start over.
5) If you got past step 4, congratulations! Now you have the fun of dealing with every single country in Europe with a navy repeatedly attacking you for the next two centuries like clockwork because the AI is hardwired to consider you an easy target due to your religion even if you own an entire continent and outnumber their forces twenty to one.Westernised Inca Empire owns everything from Patagonia to Arkansas? That's okay, OPM Pommerania is still sure they can take you.
I'm not even going to get into stuff like, say, how fun it is to deal with rebels as a native in EUIII.
Yes, in the most technical sense of the term, they were "playable". There are reasons to consider them "unplayable" that do not involve "I can't conquer Europe with them easily", as I would have assumed anyone who has played them in EUIII would be aware of.