On 6 - 8 hours a week I can never get north of a FTP ~ 260, tried increasing TiZ and various other things but time is the limiting factor.
On ~ 12 weeks per week I can get a 280 - 290w FTP, about 4.5 w’kg if I am careful with my weight.
From my N=1 and the other posts above I agree more training time will get you beyond your current level. Still need to get the recovery dialled though.