Clients are usually not hiring engineers. They have opinionns on management, on what should be done, on how you should work and in which conditions. They have opinions on you being remote or not, on how you should look like, on your mental health (cf. some pieces on whether people on the spectrum make better employees).

Most of these opinions are not grounded and you can not leverage the related tools to improve the work process.

How surprising is it that, given how few variables we are left with, these variables are heavily over-engineered?

I guess.

Those restrictions you describe are classic hallmarks of a toxic workplace IMHO, and somewhere I would leave as soon as I had the chance. I guess I'm lucky to have that choice.

Assuming your field is web development, what is not a niche skill? It seems the choice of backend frameworks is somewhat fragmented with no clear default winner.

I'm not sure there's an outright winner, but RoR was the hot thing what, 12 years ago?

It can be difficult to recruit for now.

(Also no, I'm not in web development, I have just observed this)

I'm not a Rails developer myself, but definitely noticed a lot of demand for Rails work in the various remote job newsletters I'm subscribed to. Can't say how much is legacy vs greenfield or whether this is a reflection of demand for a niche skill or that Rails is still a popular choice for companies. Either way, makes me regret a little I didn't stick to Rails development years ago as it seems quite lucrative even today.

RoR is absolutely not a niche skill-there a huge companies using it (GitHub, Shopify), tons of conferences on it (and a lot of Ruby conferences are heavily Rails), and my company personally has had no trouble recruiting devs. StackOverflow puts it at 8% absolutely popularity while Express is at 17%, so just little less than 50%, so it’s not niche just not in the top 3 backend web frameworks.