Spiky Spike

This build allows Spike to chip away at ranged brawlers and survive assassins.
I like Spike's Life Plant gadget because it helps against snipers which is one of Spike's more significant weaknesses. The other gadget is good for heavy offense but I feel like Spike isn't the best brawler for that.
Curveball is incredibly useful as it allows Spike to hit seemingly blocked regions with ease. The better sweeping ability clears bushes well and increase unpredictability. Learning to dodge curveball requires extensive practise but it can be done.
The mythic gear because, well, its a mythic gear.
The shield gear because Spike can stay out of damage for long enough for the gear to be useful and once spike is locked in ferocious combat, the other gears aren't going to be that effective either.
It is easily underestimated how much damage Spike can do at point blank range. Tanks that start chasing Spike quickly realize that their health is getting drained much faster than they think and that they have to retreat. However, Spike is even better at chipping brawlers to deny them healing. A shot in the approximate direction of an escaping brawler will hit them more often than not. Spike's super is mostly used when the opponents' team is grouped together but it also works well when Spike is ambushed. His hypercharge may not seem like too much of a boost, but that extra area can destroy enemies that would otherwise have been able to escape.
The strategy in modes like knockout or bounty is to first locate the enemy by shooting one or two times. Always keep ammo sufficient during scounting, otherwise you risk succumbing to an ambush. Hiding in bushes isn't really that effective since you're always revealing yourself by firing. However, if you do realize that the opponents' snipers are on you or you're low, hiding is probably the best option. Once the opponent has been located, keep up the pressure until you can sense the opponent about to lash out. Then, use your gadget and retreat slightly, firing rapidly if the opponent comes into close range. Use your super whenever necessary.
In the difficult situation where the opponent mostly consists of long ranged brawlers, its probably best to let any counters in your team deal with them while you unload your ammo when they're not targeting you. In the unfortunate event that even this is not possible, utilize hiding -> coming out a tiny bit -> shooting -> going back into hiding. Any long range brawlers that get annoyed and come into close range, treat them as if you were an assassin.
Finally, even though you should never be low on ammo, try to keep firing and not remain on full ammo unless you're healing. Spike is one of few brawlers that have decently fast reload but whose attack can cover quite a large range and hit unexpecting opponents.
btw one other thing I didn't include before: lobbers. Beware of them. They hard counter,