Accuracy is but one driver for running one’s own stratum 1 server. Independence from external NTP servers can be another one that, depending on circumstances (e.g., frequent network issues, or unreliable upstream servers), might be even more important than highest accuracy.
The main issue with USB is higher offset. That can mostly be compensated for.
Anyhow, PPS via USB was primarily meant to avoid dealing with the device tree from the outset, you seemed skeptical in that respect. It’s obviously up to you whether you want to go straight for that, or take it slower, albeit a detour. As said, I’d think the device tree stuff should work. It’'s simple enough to configure to just give it a shot. If it works right away, good. If not, still time to reconsider how to approach this.
And USB still seems a valid option for the NMEA part if one is looking for autonomy/resilience. If that is not a goal, using an upstream NTP server instead, as suggested by @apuls, would be even easier.
So it all depends on where you want to go, and what your preferences, interests, and constraints are as to how to get there. Just showing you some options. YMMV.