I would do the following, to clemency and all Paladin 'spells'.

1) Make them not spells. This means they would scale off skill speed. Only paladins right now weirdly have role based actions that scale off different stats, one of which you cant get.

This would solve the issue of being interruptable, since it would behave like flash. Keep the mana the same (it costs a lot, I know, but I think this can be offset with higher mp gain from riot blade) and if treated like flash would cause it to be combo friendly.

As for other abilities.

2) Shield Swipe should have its potency lowered, TP set to 0, made OGcD, given a 6 second CD.
3) The DoT From Circle of Scorn should stack up to three times. In addition, blocks should have a chance to reset CoS and set its casting cost to 0.
4) Moving between stances should be an OGCD that does not break combos.