I Am Feeling Unfaithful - but I can live with it.

[ameerat42]

I must own to a bit of TL;DR, AK, but at first I had a similar reaction to the statement you cited.
But then I dismissed my reaction to it because I couldn't "figger the statement out".

There were a couple of puzzling aspects:
1) What was the lens? - From the price quoted I thought maybe a Sigma 150-600 C (not Sports),
or perhaps the equivalent Tamron. (This, though, didn't intrinsically affect the statement, apart from
there being a large sum of money involved and some justification for the expenditure at issue.)
2) What did the seller really say/mean with "the higher the Cmos the better...", AND, what did TFK
understand by this?

OK, that may be three points. So I tried an interpretation along these lines:
If you have a "higher MPx-count sensor", you might get better results with the lens because you will
be able to resolve more detail than if you had, say, a much lower MPx-count sensor. Again, a surmise,
and it doesn't take sensor physical size into account. And then the corollary: You wouldn't need such an
expensive lens otherwise.

In that case some veracity may be ascribed to such a statement. - But further conjecture would be
pointless, - ie, academic/a waste of time/etc.

So I stopped "worrying " about it.