I doubt even the most fundamentalist or intolerant Buddhist would lose their equanimous blob over someone using stairs, frankly.I never claimed that somebody wouldn't find my tramping up a dark, steep staircase in the cliff, built by the creators of the Buddha, objectionable. Anyway, I'm sure the people of that religion who left the Bamiyan valley in the 8th Century are grateful for your concern.
It may be wrong to generalise; there may be cultures who find stair climbing disrespectful of their founding holy figures, but I don't know of any. So I think you're alright there; no-one need fret about whether or not anyone would find your use of stairs objectionable. It would certainly be laughable for anyone to suggest that you might think twice about using stairs out of consideration for the deep veneration Buddhists feel for the Thus Gone One. The very idea!
No: it's treading his head underfoot that might upset some people.