Life cleric can't tank, though - not while putting everything into healing. To tank effectively, you have to be a threat - the life cleric would be standing there just healing themselves - in other words, they can be safely ignored. Your variant paladin has all that survivability while still doing paladin damage. And assuming they don't need to survive for 20-30 rounds (when do fights go that long?), you've also given them a huge offensive boost.
So let's say we just leave the survivability of the 2014 paladin at level 20 (100 HP worth of LoH). Your variant paladin still has 280 extra points of LoH that they can turn into smite damage - that's equivalent to 28 level 1 smites, but you have actually buffed smite, so that they can do 6d8 smites 9.3 times - the current paladin can only get to 5d8 by burning a level 5 spell slot twice.
So you've created a monster tank that can choose to have incredible survivability, or incredible offence, or whatever combination of the two is needed. And that's assuming you limit smite to just the bonus action, per the 2024 rules; it's unclear from your description.
I don't think this is at all balanced, and I think the last thing paladins need is a monster buff.