Well it depends on the game. In a game like COD there is no point locking weapons but battlefield locking weapons does make a huge difference and the weapon you use can balance the game. Example:
Recon with a bolt action rifle is usually played as sniper (optimal) but you can use a lower scope for close combat, it wouldn't be optimal as the reload will more likely get you killed. The balance comes from using distance properly. if you play as a long range sniper, you are not capturing objectives and how effective you are on the field will depend on the terrain and your ability to spot enemies and remain hidden (it consumes a lot of time)
Recon with a DMR effectiveness will depend on the scope you use. You can be good at long or short range but it takes more hits to put down enemies unlike the bolt rifle. Smg, assault rifles are more effective at close range and you can drop more enemy per clip (will depend on player skill). Balance here is that you give up range and lethality for a more versatile play style
There are more things that can make weapons account to balancing like accessories, ammo quantity, rate of fire and so on. I wouldn't dismiss as not balancing as some classes are more effective in their engagement, assault is better at engaging other classes on close quarters, support should be better a suppressing crowds, recon better a long range. (Engineer is better against vehicles but it doesn't count as it uses its gatgets instead of weapons for this analogy)
Its this style of rock, paper & scissors approach that makes this games stand out from others, there are advantages and disadvantages to use certain classes. The players its supposed take it into account and find a way to better approach every situation it encounters (retreat is an option) not just play the same way with every class
For this reason I think close weapons should be the way to go, with a hybrid version as optional. Just don't want to see every fps game end up playing the same way
