A good office chair should last 50 years? A dining room set, sure, but an office chair is closer to white collar work boots than traditional furniture.

A decade seems reasonable to be honest. In order to be comfortable and ergonomic for ~8 hrs a day the chair will inevitably have some soft components that wear out.

Um... yeah, I disagree. No cushioning is going to survive for 50 years, and something like an office chair should be rotated far sooner than that (or maintained with replacement cushioning/support) to keep the ergonomics intact. Especially for an office chair (assuming this is something like an 8-hr chair and not a short duration task chair).

Then be prepared to pay 10x the IKEA price.