Clemency has been around a long time. Players generally were more agreeable to the idea of sacrificing damage for utility in 2015 than they are now. I think that it makes sense to update it so that it matches up with more modern action design.

It makes sense thematically for PLD to have a cast heal spell that they can use on demand. I don't think that it should break combo, because both the MP cost and the cast time already penalize you for using it. There should be conditions under which it occasionally becomes instant cast and free, so that it's not just sitting there waiting for a rainy day. It also makes more sense than having your healing come from vampiric effects on Holy Spirit/Circle, which have very similar heal potency/MP efficiency to Clemency when used for personal healing (0.4 potency/MP vs. 0.5 potency/MP).

Cover's main issue historically has been is that it has been uniquely powerful in breaking mechanics on certain fights. It's also iconic, so they can't just get rid of it. I think the easier solution is to change the effect to match with earlier games in the series, such that you take damage on behalf of said teammate only if the attack would otherwise kill them. Then upgrade it into Intervention and merge in the effect.

I will say that, given the number of players on this subforum who have repeatedly flagged PLD as being both 'overly complex' and having 'button bloat', I suspect that the dev team will have a specific interest in targeting those two 'problems' in the coming patches, much like they've been doing for certain DPS jobs as of late. Especially because PLD is usually the very first tank that new players are going to encounter when playing the game for the first time. I personally think that 'complexity' in particular is an overused term.