Well I don't think they are problem, without alts I think game would be too limited. Anyway i'm pretty sure there's no way to stop alting as it is.
Limited? You can get everything from other players, besides it's completely possible to make fighter crafter. The problem is just the high potential of chars forces players to arms race because character build has so high role in pvp.
Way to stop alting would be to lower the potential to be good at one thing and raise the floor to suck at something (who wants to play a char with 3ap?).
Then make it so that it's more productive to play one char long time rather than many chars short time. And I don't mean higher level cap, but for example reputation. The more you do, the more you get rep. Rep unlocks nice stuff which you cannot get otherwise for that character only.
Something like oh you can be really good at using big guns but you cannot make weapons... At least in other mmos the merchant will always have a gun you want with plenty of ammo.
You can buy the weapons from other players, this is multiplayer game after all. It's just that we don't have a nice player-player trade system. And what's stopping you from being crafter-fighter? It's just that we don't have a nice player-player trade system. And what the hell? Gunrunners, Jacob in hub and san fran shopkeepers all sell lsw, plasma rifles, rocket launchers and miniguns.