IMHO, this also applies if you want a research career. At the end of the day, you eventually need a permanent position. Most professors at top UK universities got established in Academia by doing a PhD and getting a lectureship straight after their PhD or sometimes a postdoc. Lectureships demand significant research and teaching and supervision experience.

A high-end fellowship like the ones you mention is also fine if you want to improve your publication track record. In some fields getting a lectureship after your PhD or postdoc might be extremely difficult as the market is too crowded.

>> At the end of the day, you eventually need a permanent position

Yes, unfortunately. I'm not saying it's easy, but from what I can tell it's possible: you can have your entire academic career as a long string of fellowships.

>> Lectureships demand significant research and teaching and supervision experience.

Yes, but we know that in practice what that means is that the professor leaves the research work to their PhDs and post-docs, and then puts their name on it at the end. Sometimes that's because the professor has run out of good ideas, sometimes it's because they don't really care, most of the time it's because their lectureship duties leave them without enough time to do it.

This was not my experience during my PhD, btw, my supervisor (who is retiring next month, three years after supervising my PhD) was an active participant in my research and he had his own totally hands-on line of research that he pursued separately ... and whenever I told people about that they were full of surprise. "Don't tell me that he is still coding?". That sort of thing. People were surprised because that just doesn't happen.

>> In some fields getting a lectureship after your PhD or postdoc might be extremely difficult as the market is too crowded.

I've had an offer that I turned down because it was in China, and a discussion about another in the UK that I didn't even consider. Teaching is the death of a research career, that's what I've seen and I'm not going anywhere near it. What that means I don't know. It's possible that my research career is already over anyway- next week is the last of my post-doc and I don't have anything lined up after it :/