Sure, because there's a positional adjustment: a QB is simply worth more than an RB. A 99th-percentile RB may be worth the same as, I don't know, a 50th percentile QB. That needs to be factored into your rankings. Note that this has nothing to do with team need.
Right. And if a QB should be the BPA at their point in the draft, they should be working hard to trade down. Which the Titans already have. If they can't trade down, then yeah, they may have to take a lower-ranked guy. Not demanding absolute purity here.
But really, QB is about the only position where this is an issue. Tailback maybe, too, in the first couple rounds, if you have a top guy in the first couple years of his rookie contract. For just about every other position, you should be able to find a way to use new talent, especially if it's top talent. The number of times where (a) there's a single clear BPA, who (b) plays a position at which you're absolutely loaded, are going to be extremely rare. So it's not worth worrying about too much.