Rogues when they can't sneak attack
I have to agree with the Rogue thing.
When they can't sneak attack... yes there are "things" they can do. Throw caltrops. Tanglefoot bags. UMD (maybe, if it works) some wand or item. You can be clever as a rogue and help flank and trip and be a pain.
But bottom line: if you are not doing damage, (and a rogue - sneak attack = trivial damage), you are treading water. Yes, you can help. But not very much, not on a consistent basis.
It's much worse as the levels rise. Not only are 1/3 of monsters immune to sneak attack, but enemies start casting spells/have abilities which also nullify sneak attacks (simple blur spell, fort armor, other concealment).
As levels rise Rogue become increasingly binary. Either then can sneak attack regularly in a combat and do lots of damage... or they can't, and are ignorable.
At high levels (15+) any reasonably intelligent enemy with standard equipment can be immune to sneak attacks most of the time.
At very high levels (18+) there isn't any excuse (barring a suprise ambush) for any slightly intelligent and capable monster to get sneak attacked ever. Between spells, buffs, items, etc. stopping sneak attacks is trivially easy and the payoff is huge. (not just vs. sneak attacks but, of course, for other reasons as well).
I'm exaggerating a bit... but no other class is so easily nullified as the Rogue.
Imagine if 1/3 of the monsters in D&D were totally immune to spells cast by wizardly types?
And that it was pretty easy to cast a spell or get an item which then rendered you immune to spells cast by wizardly types?
That's kinda the Rogue's situation.
(as a bonus, skills get less important as levels rise and magic becomes increasingly common and all-powerful).