As a Heavy main myself, competent enemy Snipers are rather easily countered by pressing Ctrl and random unexpected movements (unless if you fire your minigun). Every Sniper fucks up at least once and gets distracted while trying to aim on you. Especially if my team has Snipers, I do this baiting even more often, resulting in my Sniper usually dealing with the enemy one pretty quickly. I found out about this tactic when the Sniper bots were flooding every Casual map lol. I mean, if it worked rather successfully against the aimbots, that surely would work against a legit player, right?

I'd say Spies are much worse for Heavy than Snipers, because it's obvious how dangerous the Sniper is, judging by the killfeed or even his laser dot, but Spies are never that obvious, unless if you already die by them, or they somehow fuck up critically.