Not literally…for example (some are going to say it’s a really bad example, but) in TF2 the only class who can spam grenades is the demoman. Now, as much as I like or hate that game I can relate to the thinking that brought Valve to limit the grenades to one class. It was to avoid players spamming them all over the maps.
Now, I still have to play DB, but if the maps are medium/small sized I think is a pretty good choice to limit the number of mercs who can use guns (maybe not just 1, but to 2-3 mercs in the final release), if the maps are big or really expansive, maybe it could not damage the pace of the game that all mercs can use them.
BTW; obviously it’ll depend ultimately from what the devs have in mind for the fights in the game.