The Crimson Binome
Hero
Exceptions are not necessarily good. Everything better requires a change, but not every change is to the better. Rules are in place for a reason, and should be followed unless you have a specific reason to change them.1. Disagree. Rules are made to be broken. Exceptions are always going to exist and can produce some fabulous mechanics.
For the purpose of resource management, there is no difference. You're still draining two spell slots on your turn, whenever you feel like it, in addition to anything you cast as a bonus action or reaction.2. There's a difference between casting actual spells on a turn and using an ability that converts a spell slot to extra damage twice on a turn.
Flavor is a matter of perception and expectation, but a unique mechanic does not fit well mechanically almost by definition; it's inconsistent with other mechanics, to no real obvious benefit. It is uniquely powerful, so either it is over-powered, or every other similar feature is under-powered.3. IMO Paladins smite feature is probably the best designed feature in the game! It has perfect flavor for the class. It fits well mechanically. It's new and innovative for D&D.
This is a real point, but the stated assumption - whether or not it was originally intended as a balancing factor (which I am inclined to believe it was) - does not hold in practice. Due to poor implementation of Bounded Accuracy, the Paladin is likely to have a much greater than sixty percent chance of hitting. In fact, in the context of boss fights, the Paladin is even more likely to hit since there's every incentive to go all-out on buffs and de-buffs.4. As far as rate of use concerns go. Paladins get 2 attacks. To use divine smite twice he has to hit with both attacks. There's some turns he will miss both attacks and not get to use it any. The most likely thing to happen is that he hits with 1 of those 2 attacks and misses with the other. So while he is not capped at 1 divine smite per turn, it's not like he's getting significantly more than 1 divine smite on average per turn. If you want to talk about how bonus action attack feats mess with that balance or multiclassing messes with it then I'm all ears. But the feature controls its own usage rate under the basic class assumptions of 2 attacks per round and having a 60% chance to hit most enemies.
A class that's great against bosses, and not-so-great against trash, is not a balanced class. This has been evident in every edition, with the possible exception of fourth.