That's part of the point of using Linux -- not creating an ecosystem from scratch.
Virtually all of my computing outside of my phone is already done on Linux devices, and the setup works for day-to-day computing. Support is good enough for me. What makes you think Pinephone going to have worse support than my current Linux desktop?
My hope with Pinephone is that a decent influx of Linux phone users will improve the quality of desktop software on Linux as well, since it forces devs to stop ignoring touch screens and to start thinking about responsive design. Ideally, the desktop versions of many apps should scale on interfaces like this without needing to be rewritten. But regardless, I'm still not particularly worried that my bank website is going to stop working.