ph0rk
Friendship is Magic, and Magic is Heresy.
I've played a wizard. A high level wizard over a campaign. I hated it precisely because of the nuances I had to explain to Flamestrike. These cool combinations seem amazing at a glance but with so many rules and interactions, you can mess it up and waste multiple turns on something that was doomed to fail from the start.
By that reasoning, a champion would be preferable to a battlemaster or eldritch knight. And that's okay - not everyone has to like playing wizards or other casters. But watching one (or doing it yourself) utterly trivialize an encounter with a single spell makes it hard to take arguments that question their flexibility seriously.
Really, if folks aren't jonesing for an area effect blaster by mid/late tier II, I can only assume their encounters are designed especially for single target martials. There's nothing wrong with that, but if people put fingers on the balance scales with such a heavy helping of DM fiat, they should be honest about it. Setting up a gotcha exhibition match with 1-2 enemies of high CR is not being honest about it.
Look, a level 12-15 battlemaster can solo a Purple Worm. They have a small to moderate chance of failure, but a pretty good chance of success. But if folks can't recognize the entire setup is designed with a battlemaster's capabilities in mind, they are missing the meat of the difference.
That same battlemaster would have a hard time with an evil necromancer's undead army (just the army, not the necromancer herself). To equal the XP value of one Purple Worm, that battlemaster has to stand alone against 55, 75, or 260 skeletons (depending on which CR to level calculation you choose), equipped with shortswords and shortbows.
That Battlemaster goes down like Boromir.
The reason is action economy, and it is addressing the problem of action economy with multiple enemies that makes casters (blasting casters, particularly, but control casters too) important in combat.