Well, so is "better."
I've played too many 34" scale 5 stringers with all the features you note above to continue to believe that it's necessary to go 35". Companies like Fender, Sadowsky, EBMM and AC, among others, have no issues building a good 34" 5 string.
Sorry, but you completely missed all the important points. Even the ones I purposefully put in bold.
Let's try again:
All Things Being Equal..., for those that want the most sustain and piano string like modern tones, 35" will be quantifiably, measurably better.
All things being equal, given what we know about string tension between two given points, it is physically impossible not to be better given the desired result.
Nobody said there aren't good 34's out there. 35" or more is just going to be better
period with
all things being equal for the crowd that wants that desired result provided above from their instrument. Assuming they are physically adept enough to handle the larger scale.
If you're not going for this side of the tone/performance equation, you're right, 35" or more is probably not "needed". Probably not even 34". But if you are, it is undeniably "better"
all things being equal.
Most upright players will tell that full length (4/4) basses,
all things being equal, tend to
sound the best. But the physical playing issue creeps in so that is why most tend to use 3/4 basses instead. That's where the point of diminishing returns requires a trade off, not because the 3/4 sounds just as good.
No concert pianist, given the choice between otherwise identical concert grands (insert manufacturer), chooses the shorter model.
No concert harp player,
all things being equal, thinks the smaller models sound as good. We could go on........