Let's not forget what SE considers a nerf. Vishap had a LOT of HP (can't find the exact amount, surprised that's not listed somewhere) and there were quite a few times we lost with him at 1-2%. Shaving off a few thousand HP would have prevented those losses.

There were also some problems with UI in this fight. One player who used a controller said she couldn't run canons because she'd get locked in and "stuck" on the canon controls and couldn't run away when Vishap started blasting the canons, so she'd invariably die. One guy running the towers missed the first one every time because he wasn't able to see the red ring on the ground.