I know there's some contention on this at the paizo forums (especially with Pathfinder Unchained announced) but I still contend the PF Fighter, from experience, is a very powerful and versatile class for front line fighting. For 3e and 3.5, a bit less so, but i've never known a Sword and Board or great-weapon fighter to be useless compared to a "CoDzilla" on the front line.
Most important thing: if your DM is allowing the party to dictate the tone of fights and when they have them at all times, allowing the cleric or druid to "nova" or prepare only the specific spells for buffing that they use, then yes, the fighter will pale compared to a high level magic user who is prepped to be a front line warrior. However, spells run out. Righteous might and enlarge person and bull strength only last for rounds or minutes, not hours. Two or three fights in, they're spent or close to it -- or if it's a surprise fight it takes them two or three rounds to get that way. A fighter's feats usually have a casting time of a free action.
A Fighter's Feats aren't remotely comparable to spells like Enlarge Person, Bull's Strength or Righteous Might, though, that's the problem. The latter in particular would be worth about a dozen Feats, were it a Feat. +4 STR/CON, weapons increase a category in size (massive damage increase in many cases), +2 AC, DR5/Evil. Any one of those bonuses would be considered wildly excessive for a Feat and "unbalanced" and so on.
I mean, as I alluded to upthread, actually, it wouldn't be. It would be fine to have Feats that gave +2 STR or the like if they were restricted strictly to full-class Fighters and so on, but the problem is, PF doesn't do that - the paths and the BAB restrictions and so on help, but if a Fighter can get an awesome Feat, so can a Cleric. A Fighter might get 3x more Feats (seems about that, I forget exactly how many), but that's not enough to make up for the issues.
Spells do indeed run out - but by level 10 or so, they don't run out for, as you seem to suggest, 2-3 encounters. 4 encounters/day is pretty much the maximum 3.XE/PF were designed to sustain. A Fighter can keep fighting beyond that, definitely (assuming Wands of CLW to keep him up and so on), but when the Cleric, the Wizard, the Druid and every other semi-caster and hybrid is out of spells, or low on spells, and only the Fighter can keep going meaningfully, it's going to take extreme circumstances for the party to go on.
Now, I don't mean to be down on the PF Fighter, but here's the thing - he's an upgrade from previous Fighters, but PF's Casters got upgrade, too. Spells saw some slight nerfs (as did save DCs), but overall, they lost a tiny bit of power and gained a ton of versatility. At lower levels, that's still not going to invalidate the Fighter's "WHOA THAT'S A LOT OF FEATS!" factor - up to 6/7 the Fighter may well still be the main dude to be feared - but once you get much past that, not even the PF Fighter can sustain things reliably. 10? Maybe he's still solid. 12? 14? Yeah...
Of course my experience is that most 3.XE campaigns peter out by around those levels, or even end, so if you're expecting that, then I think Fighter is absolutely fine.
