Ruin Explorer
Legend
Well, yeah, it’s entirely situation dependent. If you have melee-only enemies, a third level spell would be, IMO, a good (if boring) resource tradeoff to avoiding HP loss and having to use other resources. If it’s a different kind of enemy,you’d use a different resources. At the end of the day, combat is how you use your resources to get the other guy to 0 hp before he does the same to you.
Sure, I guess my issue with fly-n-plink specifically is that Fly hits one PC and doesn't offer that much benefit in most scenarios. It's the sort of spell which would be hilarious in a computer game, with predictable AI and enemies who definitely couldn't attack you, but in actual D&D, with intelligent enemies, run by a DM, it's much less likely to be viable. You can get one PC airborne, but even animals will likely scatter and either hide or flee (animals understand predators that come from above), and intelligent enemies will take countermeasures, which could be anything from running for cover to throwing rocks or even tricking you into some sort of foolishness. You're unlikely to get more than a couple of rounds of attacks unless they're on a big empty plain with nowhere to hide/seek cover. And it's only one PC at 3rd (+1 per extra spell level), so either the rest of the party has to fight as normal, and you're just avoiding/lowering damage on one PC, or they have to sit it out, meaning the enemies likely escape (quite possibly to return later). Sorry to go on about this - I've played a flying PC recently and I've seen that this sort of thing is a lot less effective than one might wish (it's another story if the entire party is swooping in on griffons, of course).
Whereas hitting the same enemies with a Fireball (or similar) and just charging in and fighting them normally is likely to cost only limited HP, which are fairly easy to regain for most parties, given HD usage on Short Rests and so on.
It's the sort of false economy I'm discussing, actually. If the PCs never need to use HD, for example, because you expend a lot of spell slots doing elaborate and fragile stunts like fly-n-plink, that's actually kind of a waste, or at least isn't helping all that much. Ideally you balance usage of all the resources the party has. It's rarely possible to do it perfectly, but often possible to do it well - for example, in the group where I play a Druid, I don't roll out the healing spells just because people take damage - we use HD first (until approaching the 50% HD cap regained on Long Rest), unless it's vital to keep someone up (or get them up).
I think this illustrates another issue though, which is that in certain situations, peculiar corner-case solutions will be valid (as with True Strike and Plane Shift - it's not ideal but it's no worse than getting someone else to use Help with their Action). With a single physically-large (i.e. preferably H or bigger) enemy, of beast-level intellect, in relatively open terrain (plains, rocky hills), but who is extremely dangerous in melee and is tough, and who has relatively low move speed (preferably 30' or less - at 40' or more he's going to force you to use a lot of Actions to Dash instead of attack, and at 60' he'll outrange you quickly unless terrain prevents it), that could be really optimal - so long as you can kill him in under 10 minutes (which to be fair, if he can't outrange you, you almost certainly can).