I do agree with this. Most systems have significant basis in unnecessary or outdated methodologies. I think with the JWST project (with partial hindsight), we probably could have benefited from having a "stepping stone" optical telescope after Hubble which we could have used to proof out some of the hard parts of JWST. We learn quite a lot from just running missions beginning-to-end, and extremely long cycle times sacrifice this learning opportunity. It also means that we focus less on developing extensible "platforms" in favor of one-of-a-kind systems which have somewhat less carryover knowledge for the next project. Shorter mission timelines mean that you can better leverage state-of-the-art technology, rather than being forced into a design which constrains you to decade-old technology.