as long as you do not need single core performance the M3 should actually be fine - the price jump to the M3-Ultra versions seems justified
And let's put that in perspective too -- the M3 is no slouch when it comes to single core performance. The M4 is of course 20% faster than the M3 but the M3 is >10% faster than an M2, all of which are faster than the fastest computers from a few a years prior. Even on single core applications, M3 Ultra buyers will not be suffering. If someone only needs to run single core applications, the M3 Ultra will not be cost efficient but it's not like the system is going to lag.