Kurotowa
Legend
It seems to me that there are three seperate issues being discussed in this thread and it would probably be useful to treat them seperately.
1) Are Martials able to keep up in their key area (damage) when compared to casters?
2) Are Martial characters duller to play in combat because of the smaller range of options that they have?
3) Are Martials lacking because they don't don't have anything like the caster's utility out of combat?
These three things may all be true, may all be false, or may be true in some cases and false in others. They are not really intrinsically connected.
For me, the third is definitely the biggest issue. Combat tuning is hard to pin down because it's so context driven by the adventure and the DM and the party composition. Dullness is a subjective value judgment about playstyle, and different people enjoy different things. But narrative impact is, to me, an issue with a clear divide.
A high level spell can transport a party across great distances, summon angels and demons, raise castles out of nothing, re-write the minds of the weak, and divine the secrets of the cosmos. Meanwhile a high level Rogue can reliably succeed on skill checks, which many DMs limit to a far stricter standard of "realistic" outcome, and other martials get nothing to do at all. Even in combat, casters have options to reshape the battlefield in ways that martials don't.
Maybe the solution is to give high levels martials access to a pool of special abilities, like an intimidating aura that cows the weak or the ability to parry spells with a slash of their sword. But, and this is an important part, it has to be at least as distinct from the caster spell pool as the Cleric spell list is from the Wizard one. If not more so. And then future books have to carefully toe that line so as to not homogenize the ability pools. There can be a little overlap, like stomping the ground to create an Earthquake, but what martial fans really want is cool thing that aren't just being a Wizard with a sword.