I'm not looking at a sheet now, but I am not sure it's possible to fit in 50 heat sinks to a 'mech even if you use advanced rules to remove things like hand actuators, IIRC there's only some 34 or so critical space total in a 'mech. But anyway.
Overall that's where Mektek team developed the Hardpoint system towards as they expanded MW4 Mercs, adding new types of hardpoint slots ie there's slots that can fit ballistics or energy, or other such combinations, rather than just Omni slots for ones that can fit more than one type. With the expanded selection of 'mechs that leads to a considerably larger selection of builds.
Also I'm not talking about it like it's a problem in itself, but that it's a problem that BattleTech as an IP due to having iconic 'mechs has to deal with because its its' own elephant in the room every time around of how to handle trying to make 'mech selection genuinely diverse but without causing Hunchbacks with LRM5s everywhere because it's actually just a skin for generic 55 tonner. It's the old cake dilemma, really, and I think hardpoints are a good enough problem and I think that Mektek improved the idea considerably by adding additional categories of possible hardpoint types. It's a system that can be worked with and that provides a good answer to the problem that franchise has to deal with when it comes to iconic design vs customization. It's certainly better than what I understand MWO did (I had little interest in that because I think campaign is pretty important to MW games) by just having variants and deluxe variants, or limited customization (this I'm not sure about, just something I heard later).
50 heatsinks is just hyperbole, though when you count double heat sinks you can go quite high, something like 44.
I don't think the looks issue is a huge 'problem' especially since you are in the mech itself and can't see it. It is something to consider but not the main issue. The only real issue with omnimechs is that it can be very munchkiny. Aside from loading up on more heatsinks than any normal mech could have, you can also negate the main disadvantages of certain mechs by putting all of the ammo containers into areas where you don't have to worry about them. Usually the arms but if you are a true munchkin you will realize that putting ammo in the legs or head is even more munchkin because you lose those and it's game over anyway and they are much less hit prone and are highly armored. Then you can have lightly armored arms full of double heat sinks and all the weapons in the belly.
With a mech like that it is not hard to take on 4 powerful mechs all at once with no problems. In ghostbear's legacy you can easily take a 20 ton mech and run through the whole game because of this. Well, if you are really good you could run through them with a standard locust too but that requires real skill.
That is the main reason to restrict unlimited omnimech stuff. But in MW 2: mercenaries this is largely overcome because you can't just grab whatever equipment you feel like at all times. You can't ever get enough ER lasers for all your mechs let alone to turn them all into frankenstein abominations.
With the hardpoints system though it is kinda weak to replace an AC 20 with a gauss gun, that is not a real customization at all.
I think you could adjust that idea a bit to come up with something that works well, though. For example if hardpoints were restricted to weapon, system, or any then you could make each mech very interesting.
Marauder is my favorite mech by far. So in that case you could put say 6 weapons mounts on each arm and then a bunch of system mounts in the shell and maybe a couple 'any' mounts in both. That way you can make it so the customization does not go crazy, and also make it so you can just swap out the weapons models on the arms and ensure it all looks right. Which is not the most important thing but also desirable.
So you could make a marauder that had two PPCs in one arm and 6 small lasers in the other, and make a mech that is a brutal killer at any range.