What is quoted is a statement of preference. It is going to be hard to prove beyond a reasonable doubt that Cohen clearly lied about a preference.
Say I testified that I don't really like chocolate ice cream but you found me eating it one day. Hard to prove I lied, I can always just say that what I meant was it wasn't my favorite flavor of something like that. Or maybe I found a brand I do like or maybe I just changed my mind. But even if you could prove that I was lying when I said the statement, is that really something worth congresses time? In this case I would say no, not for a statement of whether Cohen was being honest when he said he wasn't interested in a Trump Admin job.
False equivalent. One is a statement of observable fact: did, or did not, ask WH employees about a position (several said he did),
versus your example: a statement of opinion - unable to be proven. Saying you don't like something then eating it doesn't prove you changed your mind. No way to prove an opinion. You could have been trying a bite to see what you're missing.
There are mechanisms for amending testimony. Cohen didn't do that. After you get caught lying is the wrong time to try to make amendments.
As for "worth Congress' time," this is all on the Liberal Democrats in Congress. They scheduled the hearing, because they wanted to smear Trump. They already knew ahead of time Cohen had no 'smoking gun" to impeach Trump with.
The fact he lied can't be ignored. If he'd been honest, there would be no time spent. Blame Cohen, Schiff and Lewis, not the GOP members holding Cohen accountable -- again.