It's not so simplistic.
Let's take a simpler example that is easier to highlight the problem - Overwatch.
Overwatch is much more of a system that you're talking about, where there are counters. Some are hard counters, some are soft counters- but it is much more along the system that you're envisioning.
McCree is a hard counter to highly mobile characters, like Tracer.
The problem is that his ability was too strong - it ended up being a hard counter to Tanks. That wasn't the intention of his ability. He was performing outside his area.
He needed a nerf.
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Nerfs are necessary even with counters.
The game is lacking some counters.
Snipers are outperforming for two reasons:
1.) Not enough counter-play
2.) They are too strong outside their area.
For 2 - they need an intra-archetype fix (make the low impact snipers the mobile, close, quick scoping snipers while the high impact snipers be slow, hard scoping heavy hitters) For 1, all weapons need a boost to flinch, with a tweaks to high caliber rounds and unflinching.
Sticky grenades don't need a nerf, but they need a counter. It's too easy to do a quick peak, instant kill without recourse for the other player. That isn't a fun experience.
DoT could use a counter as well.
English
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DoT- life support or red death I guess