I am not certain, but I believe plants ohmnoming heroes is a bug. With the dragons the best advice I can give is to payout the moment you realize you cannot save it. Even some of the most epic battles are not worth losing a dragon to win.
The main hero de-leveling happens to me whenever I level him, whats surprising to me is you even managed getting him past 25(he's just a glorified buff bot for me).
As for the level 4 royal you could have made a bug report on it, they restore lost units all the time so broken ones are not likely any different.
By the Lake Batman, somebody poisoned the waterhole!