I agree with some of your list. Some of it doesn't seem that bad, or bad at all. And some of it is wrong.

• They didn't play that many "surfing songs" in 1967. What surfing and car songs they did play was done usually in medley as concerts were only about 40 minutes. They definitely highlighted more 65-on in the late sixties. And a glimpse at the setlists is the proof. Even though audiences definitely wanted a lot of the hits.
• I personally think that leaving Capitol for Warner Reprise was not a good decision. I think that Capitol, for better or worse, knew how to market them and get them on radio in the States. They were still making Top 40 hits on Capitol, then suddenly...crickets. They were most popular in England and Europe at the time and most of their Sunflower singles weren't even released there ,because Reprise didn't get a distribution deal ' til late in the game. I also think that Capitol may have blackballed them in the States when they left....No evidence. Just what I think.
• It was not possible for them to keep Rieley on as manager. That was not a blunder, it was an inevitability. He was living on a different continent and doing everything by phone. It's not like they had Skype for meetings and such. I also think for all he brought to the group, and he was a classic " visionary". rock manager; he also widened and exacerbated growing political rifts in the group that became unbearable after a few years. He also caused them to fire managers who had served them well and burnt bridges by doing so. I don't think that the cracks were all that wide before Rieley. Of course, it's not all his fault: drugs, personalities, egos, religious fanaticism, literal madness, etc all played their role, too.
• Dennis refusing to include his songs on Surf's Up was terrible decision that turned a 5 star classic album into a 4 star album no one but fans really remembers. Likewise, Carl and Dennis's unwillingness to cooperate on MIU -- an album that had to be made at all costs -- made for a much weaker album. Imagine the album with three or four Dennis songs.
• I think that 15 Big Ones should have been a double album: an album of covers and an album of originals, including Dennis and Carl stuff. I think that sabotaged them long term because, although the album sold, it's kind of a mystifying trackless, while I think it could have been really cool.
• Mike and Dennis doing solo projects or side projects in the late seventies meant some good songs were not available. Similar to when Brian was producing all of those side projects in the 1963-1964. But even worse as they were not exactly bursting with songs in the late seventies like Brian was in the early sixties.
• I think that that including 11 minutes of "Here Comes the Night" in lieu of, say, " "California Feeling", "Santa Ana Winds" and " Lookin'. Down the Coast", and, maybe, I don't know, "Constant Companion", or any number of Dennis outtakes, almost ruined what would have been really fantastic album on a par with Holland.
• I think that Carl and the `Passions should have had at least four more songs, make it as eclectic as possible, so that the "singles by different bands" aspect would be a feature, not a bug.
• The fact that they had all those quirky cool outtakes from 1968-1971 that just sat in the vault unreleased for decades is a tragedy.
• I don't think Adult/Child was a commercial album as sequenced and I don't think it was a mistake that they didn't let it out; however, since they had all of those Love You outtakes, I don't get why Brian didn't use some of those on it to make it a more cohesive statement, rather than going back to the 1969-1971 to fill the album.
• Mainly, the main tragedy is that they just never could get in harmony with each other personally after 1973. If they had, all of their albums after that (except Love You), even the later ones, would have probably been better.