I think one has to weigh tankiness vs ability to deal damage when it comes to the general approach on how to gauge median power - the class only does tankiness "ok" (leech that isn't tied to MO space on your weapon together with flat +ar on solar flare is a really nice bonus) and the damage isn't anything exceptional no matter how you approach the problem (4k str 2h class weapon swinger for maximum stat scaling etc)
The skill switching is fine - there should just be a payoff to bothering with it. I do not think putting solar flare on a much longer duration would solve anything - I already have almost full uptime of both solar flare and vindicate, the end result is still the same; you could get much more for less with another character.
Because the class doesn't have actual damage outside of raw melee range you end up struggling with some gimmicks in ubers and you will never turn into a specialized boss killer like ancient hand barbarians with -170 fire because there are no tools for it, the spell oskills that are available on paladin shields are all locked out by solar flare so there isn't any hybrid potential with stacking str factor and weaving in external buttons like ring of light.
Either way, not to derail your progress further but I would be surprised if you find a pot of gold at the end of the rainbow with your holy melee dude
