Is it fine?
Take any stock model mech. Most have various issues. Let's start with equipment locations, these are very easy to optimize. Armor allocations.
And in many cases, removing a single weapon to add a heatsink, ammo, or some armor is a worthwhile trade.
Suddenly the mech is much better than the basic model.
Anyone who could do that would have an advantage.
And what is wide range of "optimized builds"?
Arguably someone will figure out the best build for a given purpose, so we end up with "best close range", "best long range" and so on.
How do you nerf those without nerfing individual weapons, without nerfing people who don't use optimized mechs.
(Arguably adding quirks like increased heat dissipation, faster ROF, more damage, and so on (or negative versions), to mechs could be used for balance, but they can also cause people to shun designs or take advantage of them too much)
Why use sub-optimal build, unless you're part of some unconventional tactics group?
In what world is a mech with mix of all 3 weapon types with all weapons for all ranges is optimal?
There are quite a lot of stock mechs that try to be jacks of all trades, and they never work as they're in Mechwarrior games (or at least they're far from optimal and can work with enough skill). At very least, one can always improve them a bit.
I cannot see non-optimized mechs to work well in a game that is basically a first person shooter.
Even random spread wouldn't help non-optimized mechs, it would actually hurt them more and just piss people off.
Just pointing out various issues with enabling customization in games in-general, including Battletech boardgame as Battlemonkey noted.
Personally i'd favor a system where customization is extremely limited: for example, one could have "customization points". Let's say each mech has 20 of them. Changing a weapon to another would cost a lot of points, whereas merely re-arranging somethings would cost less. Reverting changes would refund the points, of course.
Optimized builds are essentially ones that have taken careful consideration to reduce the amount of free slots and tonnage wasted, with an effective amount of ammo for the duration of battle, that have a small but reliably and synergistic number of weapon groups (4 max), are somewhat heat balanced, and comprised of and built around solid weapon systems.
So a 2UAC5, 4ML catapult or cataphract would perform quite well in this sense - good DPS, good back up weaponry, the ability to alpha with heat for extra damage, or use primary UAC5s to cool down.
As opposed to builds that didn't use endo steel when there was sufficient criticals, or even players that thought SHS was a good idea, or decided to bring an engine that was far too big, failing to equip sufficient weaponry, etc, etc.
I would even be ok if all the cheese builds that have been used to date would be competitively viable at the same time; because at least there's a good amount of variety there!
I'm talking about 9SL fast swaybacks, Gauss kitties, LL boats, PPC boats, Raven 3Ls, Missle boats, DDCs, splat cats, streak cats, pop tarts, etc, etc.
If those were all on the same or near the same tier of competitiveness, at least you wouldn't have to see the same thing in game after game after game. And there would be a variety of counter builds to those mechs; and more importantly, if all those cheese builds are optimized at once; it's because the weapons are sufficiently well balanced that they're all effective.
Suffice it to say, you'll find yourself in an esoteric minority of players that want to pursue a really limited customization system.
I mean, I'd love to be able to play a 3025 mode... but not if it was the only mode I could play - similarly to the limited customization system; it'd be nice to play with such a ruleset, but ultimately it would just stifle and stagnate the game even more than poor metabalancing.
And it seems like such a short sighted thing to want to mandate; essentially throwing the baby out with the bathwater - using a solution with far reaching, mostly negative consequences in order to maybe help with the metabalance issues.