I'm not going to argue what's already been said, I'll just put it as understandably as possible.
1. "People are just going to min-max and build Laser/LRM/LBX boats" - Here's the thing, those boats already exist with many currently available variants, and they're easily killed by mechs of a different sort, or artillery, or aircraft, or sneak tactics. This is not MW4 where you get 2-8 guys in a small arena to slug it out and see who's standing last, this is TEAM deathmatch with VEHICLES and AIRCRAFT as well as mechs.
2. "There will be OP setups that break the game's balance" - umm, LPL huey anyone? It already exists, and by finding out it exists the dev team is going to do something about it. Again, this isn't any older MW game where the game developer just drops the product on you, ignoring any "multi-player balance" issues. This is a multi-player-only mod made by a dev team that cares. Obviously imbalanced mech designs will be addressed.
3. "People are going to spend more time building mechs and less time using them" - I can see this complaint coming from someone who's played FPS games online for most of their gaming life, but from a mechwarrior fan? The mechlab is a HUGE part of the fun that is to be had in mechwarrior, and is one of the core elements of the "great gameplay" that made mechwarrior such a hit. If you can't understand this, than you obviously HAVEN'T played enough classic mechwarrior.
I'm almost positive that the dev team will allow for a server flag that "enables" or "disables" mechlab on their servers, and I'm sure that the mechlab system will be intuitive enough to allow for optimizing weapon grouping. I'm sure it will be easy to use too, remember these guys have played every mechwarrior game that we've played. They know what worked and what didn't.
tl;dr this thread is dumb and you should feel bad for posting it uranium.