Second Wind is a terrible ability and either needs redesigned or outright removed.

[Ransu]

Saying Second Wind is just fine when it crits just screams "Second Wind is not fine at all." So, 80% of the time it isn't very good and the other 20% it is great. This is why tanks don't have mitigation abilities that "sometimes work." Let's say that Sheltron can block 20% but sometimes blocks 0%. Is it even worth using?

Its fine when it doesn't crit. It serves exactly the purpose it needs to serve which is a small heal that would save you from what otherwise would probably be death from a raid wide. People need to get over the idea that its supposed to be this big chunk heal when that's not its purpose. It would be broken if it healed for more than it already does.