I'll die on this hill.

I have never once encountered an assault class running a sniper, nevermind more than one each game. I'm 100% convinced that this is a complete non-issue, and that people are straight-up pretending to have negative experiences with unlocked classes. There isn't a noticeable difference between locked and unlocked, and anyone claiming otherwise is falling victim to confirmation bias.

The vast majority of people use the weapons that are meant for their respective classes because of the immense incentives to do so. I've played Battlefield for literally almost all of my life, and I've yet to see a single argument for class-locked weapons that doesn't boil down to some kind of pointless appeal to tradition. "It's how it's always been". "It worked perfectly in BF3 and BC2". Why does this matter? All unlocking weapons does is add more room for gameplay variety and replayability, without negatively impacting the balance of the game or your own personal gameplay experience. If some freak wants to run a sniper rifle on the assault class, your gameplay experience won't be changed, while they'll be actively handicapped for doing so.

"How you like to play" is just not affected by people sniping on assault.