I've found fighters to be very useful. They're very hard to play, far more so than a wizard, cleric or druid.

The job isn't just to hit stuff. The job is to face off on the front line. That involves hitting stuff, getting hit, manipulating the trade off in your groups favour, and making sure you're pursuing the right options. Playing a good fighter is about what's good for the group. Putting yourself in harm's way and trying to stack your personal combat prowress is almost always a bad idea for the individual, but it gives the rest of the group the edge that allows them, for example, to play a character that's really weak in defence but has a great selection of spells. That's why, if you just compare what each can do by themselves, or worse, what they can do to eachother, you get a distorted picture.

Part of the reason why some people don't rate front-line fighters is because they play them badly. Part of the reason is that, yes, there are now enough spells out there that a spellcaster can prepare for almost any eventually. The key word there is can. The sample cleric being discussed is cloistered, has the war and trickeryand dragon domains, divine metamagic, and apparently enough rounds and spell slots to heal, buff themselves, debuff the enemy and still full attack every round. I'd love to see his sheet. Flexibility is key yes, but spellcasters have to make choices, typically at the start of the day, on what to focus on and what not to.

Take your cue from what people choose to ban. One of my groups has come up with a fairly lengthy list, including divine metamagic, VoP and polymorph, sure, but also including two-weapon fighting with armour spikes, the marshal, and some of the more egregious archer builds. So long as you avoid the really cheesiest builds, a balanced party still works better than all spellcasters, although I'm sure that's a lot of fun, just like a playing an all-rogue party is great fun. I'm not saying that the spellcasters aren't powerful, or even that they aren't too powerful, merely that if you've reached the stage of calling all front-liners useless, no matter how well played, then you're probably overstating the case.