I'm not clear which way you are arguing here. An upgrade is additonal work right? Like, an extra sprint. It turned out to be crazy expensive. The F35 programm

I'm not clear which way you are arguing here. An upgrade is additonal work right? Like, an extra sprint. It turned out to be crazy expensive. The F35 programme went wrong because they built an MVP (F35A) and then decided to derive 2 extra planes from that design (F35 B and C). Turned out that modifying an existing air frame to make it VTOL is really hard and they would have been better off designing a new plane from scratch. As you say we weren't there, don't have the data, and judging the facts from a noteably freakishly unsuccesful programme isn't sensible but... I mean, I think it supports the idea we shouldn't do this.