Thanks for your input Chris.
Two thirds of our way up the mountain was on farm tracks and quad bike trails. These were easy to follow and very cycleable. It was not until we met the Pony track that we hit rough conditions under tyre and severe erosion....and of course walkers. I lacked the talent to ride up really rocky parts and used walk mode. The final 100 feet was purely on foot with the bikes left on a grassy step.
We saw one other rider all day.
I get the point about track damage but we were nothing compared to the cumulative effect of thousands of boots.
Of course, lower down, trails in woods and the like do get a bashing through significantly higher usage.
Anyway, I hope to stick to courteous sharing on such exploits and stay away from walker honey pots like yr wyddfa!