Maybe it's player/match-up dependent, but I feel like you can definitely train to react to heat activation. I think moon drive is a little bit scarier since it's so fast. I played a ton with my friend the other night and after a while it becomes easier to stay out of range and gtfo for a free punish if you aren't too close and have access to a decent backdash. The hitbox on heat isn't really that big so it's easy to bait it after a hard knockdown.
As for guard cancel, maybe it's more of the same. Reacting to it might be possible. Anti-heat os seems serviceable enough. I haven't played enough against other players to really have a decisive opinion on dealing with it when the opponent uses it defensively like that.
But it's definitely strong, fax.