I disagree with the notion that Precision Strike as such is the problem, because PS is just tweaking the probabilities that are there anyway. Generally and depending on your angle to the target, not every mech part is equally likely to be hit. Heads have a small hit probability anyway. If you face a Mech frontally, CT has a higher prob to be hit than the others and so on. PS is just shifting the probs in favor of what you want to hit. If your angle is bad for a specific target, PS will make your probs better, but not over and above what can reasonably expected considering the firing angle.
Except it does. When you have no bonuses, you're chance for a called shot to the heat is 2%. With a Marauder and 9 tactics, it can hit 35%, or 1 in 3. So yeah, I'd say that's a pretty unreasonable increase in percentage chance. Likewise, the ability to hits torsos gets insanely high. Sure, if you're on the left side, you aren't going to have an easy time hitting the right torso. But for the rest, yeah, easy. Now, maybe you want to be able to raise the chances to hit the right side from the left side. Okay, but then the odds of hitting any particular part, including the head, ought to be capped much lower than they are.
Without the tactics and Mad bonuses in play, the to hit probabilities are overall fine. Legs from the front could probably stand to be slightly higher, matching the arms like they do from the side. That would make the higher armor there have a bit more of a point (besides DFA), plus make it less obvious to put the ammo there, but that's a hold over from how the 2d6 hit chart in table top works.
Let's not forget that other factors add to this - availability of weapons dealing sufficient damage, for example, and that's +weapons and LosTech. A stock Marauder with regular weapons isn't such a big deal, is it?
Yeah, actually, it still is. You face an Atlas with that, and you'll do 145 damage to its right torso, without figuring in the mediums. At that point, fire from other mechs is likely to take out that torso. Sure, it isn't one mech doing it all, and you aren't flat out killing the mech, but it is still quite effective. And that's with the standard "this weapon set up is crappy" stock mech. You could easily improve the Mad's performance quite a bit, without + damage weapons. Also, the LosTech weapons aren't a huge factor either, as most of them aren't exactly great. HM weapons are another matter, and one whose design decisions are questionable enough that HBS is addressing it in 1.9.
Don't get me wrong, a bunch of the + damage perks are a bit on the silly side. LRMs and SRMs get a 25% damage bonus per pip, and are allowed to get two of them. Snub PPCs get a whopping 33% bonus per pip, which is just downright silly. AC/2s, Ultra 2s, and MLs, 20% bonus per pip. And when you compare that to things like PPCs, which gain just 10% or LLs, who gain just 12.5%. It definitely is a system that favors weapons that hit for less, and allows the players to gain a lot of power. For some reason, HBS locked themselves into having a + and ++ version of damage, and for having it increase by 5 whenever the original damage number wasn't very low to start with. Probably not the best design idea. And that all combines to just give players a massive damage boost regardless. But that's a whole other issue, a general one.
Also of note, I already called out a bunch of other things that help make called shots even sillier. Clustering, especially with an 8x and 4x multiplier, was a bad idea (and another thing that makes legs the ammo storage place of choice). SRMs shouldn't see the hit location percentages changed at all. LB-Xs, same deal. And of course, how easy it is to get high accuracy, due to things like no to hit penalty for moving, no medium range, and so on.
And yeah, all the things combine to make things problematic. Weapon damage scales up. You get bigger mechs, with more tonnage for weapons and the heat sinks to let you fire them. The weapons get better. Your morale increases, and you get get +resolve head gear, making it possible to use abilities a lot more, make them part of every turn, rather than something saved. But none of that changes that I shouldn't be able to target a location and have a 75%+ chance of hitting it, nor a 35% of hitting the cockpit. Heck, the latter means a (player controlled) Marauder would still be effective in the late game if all of its weapons did a single point of damage each.
So, with a couple of things coming together it makes no sense to shift all the blame to just one thing.
But it does when that one thing is the main culprit, and as a single thing, makes far, far more sense to tweak than having to go through and re-balance half the items in the game.