Its fine to leave gaps, the latest role is the most important. The .net work doesn't add much to a DS role so there isn't much weight in mentioning it and it shows you spent less than 100% of your focus on DS. If there aren't other candidates then that's fine but there are 10s of candidates that are more or less DS-only on paper.

If candidates could see the other applicant's CVs it would kick off an arms race.

I'm not sure what you mean by DS, but I would strongly disagree that work in one stack is irrelevant to work in another.

Two years ago, I took a role in a tech stack I've never used before, and in less than a month I was productive in Node and Rails. I work with half a dozen developers that switched from one stack to another, and regularly do so to use the best tool for the job, and it's not as hard as some companies make it out to be.

Is anyone actually claiming a shortage of experienced developers in London? Or is this just what we developers would like to hear?

IMO there are few, if any, tangible signs of a shortage locally.

It depends who you ask, I guess.

There's a definite shortage outside of London, although few companies seem to want to up their salaries to attract experienced talent. One of the reasons I switched stack was because I would get recruiters emailing every day with new roles, but rarely anything that paid over £45k in Bristol.

In your experience, as a Londoner, is there a demand for experienced devs? I would've thought that big companies would always be looking for developers.

There is always a fair amount of demand, but from the way hiring companies act, one can feel they have many decent candidates to choose from.