Considering the burnout rate of my fellow non-freelancing developer friends, I would actually suggest the opposite.
Staying in a company for 1.5 years and perfecting a niche technology, while helping the company and get paid for that is one of the best sides of being a developer.
Of course you can go to a company that attracts with business/life opportunity, rather than tech. stack, but nevertheless development cycle there is usually more slow and corporate.
As a significance of "gluing" front end together, I would say that this is becoming an area of extreme expertise and yes, you can safely build your career around that.
It really depends on how great of a UX you want to provide. Create an extremely efficient backed whilst creating a terrible frontend will get users frustrated but having an awesome frontend and a measly backend probably won't.
If you're developing full stack, you have to count every attack vector and try to prevent them. Full stack is serious work, but having a backend that can defend and is efficient and a frontend that is easy/good to use takes work.
I agree. Also in this particular case, an added challenge is that the frontend has to work offline and my customer wants to self host everything instead of using an easy 3rd party solutions like Firebase, even as a proxy.
I would think that what the font end is for would be more important that the technology powering it.
I would look for a job in an industry you find intresting rather than a job that uses a tool you know.