I also fly for a major fractional (less stress, more money, and better QOL than a 121, personally :-). To the OP’s question, the majority of the situations we see in the air and on the ground (we get into our fair share of large, regional, and small GA airports equally) is that we rarely run into an instance where we interrupt, delay, or flat out cause a 121 carrier to be delayed or suffer a schedule issue. We fly higher than them by a comfortable margin, fly just as fast, and just as far. It generally isn’t a problem for us to have our PDC/CPDLC etc. issued, flt. plan entered into the FMS, pax loaded, and be on our way…all while merging nicely with the big boys at the larger airports. I’d honestly have to think hard to recall a situation over the last two years where I can remember any of our crews having such issues.
I’ve had to do several diversions over the last six months…both on the East and West coasts…and haven’t been privy to any times where we’ve delayed regional, LCC, and/or legacy 121 carriers due to our changes in plans. We’ve also had our fair share of “routing verification discussions” with ATC as you’ve described, but they’ve been resolved with minimal time and effort spent. Not sure if this helps address the OP’s original question and/or sheds any constructive info, but these have been our crews’ experiences, generally-speaking.