I usually don't bite on these type's of QQ threads that lack evidence, screen shots or any remote idea of how the classes are played.
You see "tracer, tracer, tracer" What you don't see is "tracer, 2x heat signature applied, tracer, Barrage proc, Heatseeker, Unload" All of which get their proc's FROM tracer missile.
If you took tracer to a 15-20 second cool down you would need to completely revamp the way Heat Signatures and other proc's are applied. Also, without adrenals, etc you will NOT get constant 5k+ crits, I'm sorry it just isn't so.
Basically the entire Arsenal Tree revolves around Heat Signatures... How do we get them... ZOMG Tracer Missile!! So rather then posting the countless "**** nerf this class, nerf that class" Learn how to play against them, play smarter and don't get tunnel vision and be surprised that the Merc/OP/Sorc, etc that's unloading on you from the side/behind is killing you!
tl;dr Revisit how Heat Signatures get applied for Merc's. Tracer can be interrupted and is avoidable and doesn't do CONSTANT 5k+ crits.