I’ll actually go against Peci and say Frost Mages are the best caster in the game right now.
A single melee shouldn’t ever really be able to touch you as Frost. You can still 1vX but it’s very hard, everyone has every tool these days. Against highly skilled people it won’t happen, against your average player or even worse, someone from Ruin Gaming, it’s actually fairly easy to pull off (fun fact, I kill 4+ RG members at the same time in BFA almost daily.)
Fire is extremely high paced and dangerous, but also tends to be squishy at times too. Arcane has no instant burst but can be VERY slippery for Melee to get in touch with.
Locks will likely still win that match up. You’d really have to play everything to a T to win. They’re quite tanky and if played well, very annoying to try and control. A big issue is stopping the fear -> bolts or X -> bolts. You’re doomed if you kick anything but bolt, but a good lock will likely never cast bolt until Kick/CS is on cool down or unless they’re safe from it being locked.
Mages in general are still top tier in skirmishes.