Paladin isn't the best at staying alive solo =/. I've solo tanked plenty, on trash NMs where it's feasible to do. But if we're talking about trash NMs, plenty of jobs can stay alive and keep hate better than Paladin.

The harder any given NM is, the more of an advantage PLD gets in the Enmity game because everyone else is able to do less and less damage for Enmity while taking more and more. By the same token, when you hit an NM that's too hard for a DD to tank with damage-Enmity, Paladin (and no one else, really) should not be tanking on their own.

Can I do it? Sure. I've tanked plenty of hard stuff solo when I had to. That doesn't mean it was anywhere near ideal, or easy, or practical, and I wouldn't want to do it again in the future. People figured out years ago that the ideal way to tank any difficult mob was in pairs. Any more would become too complicated to manage (unless the NM could insta-kill people fairly often or something, and even then that was 2 at a time + rotation), while solo tanking was just way too dangerous and lead to significantly more deaths. Hell, with anything that is legitimately difficult to fight, solo tanking may as well be impossible, that's how much you're gaining by having 2 tanks that work together well.

Any ability that takes away the ability to work properly with your co-tank is useless at best, harmful or even wipe-causing at worst. Besides, Provoke is fairly useless at it is and still requires /War which in and of itself is pretty bad.