Yeah, there are pretty good options for 26" rims and tires yet. There are other standards that are far more "obsolete."
My hunch as to the OP's problem is that his tire choice is letting him down. Perhaps the wheels themselves are also heavier than ideal, or the fit is off. Drop-bar MTBs can pose challenges for fit, and we all know that fit issues can rob power output.
Basically, everything that @
HTupolev said.
