I went from Playbar, Sub gen 2 and 2 x Play 1 to the same setup as you now. You are absolutely right, that was also my first experience. I have held countless parties where the volume was set very, very loud with my old setup. Arc Ultra can't keep up. However, I experience a much better/cleaner sound, and after a while I didn't think about it at all, on the contrary I value quality much more than volume.
You will NEVER get Arc Ultra to play as loud as Playbar, the speakers inside are not big enough at all. They were about twice as big in Playbar as in Arc Ultra.
The only thing you can do is turn up Arc Ultra/Era 300, depending on how dominant you want Ultra/Era 300 speakers to be in your setup. And then of course set Era 300 to full during music.
Is it with both TV/Movies and music that you experience challenges?
I really do appreciate your response. I have also discovered the gen 4 sub is much lighter than earlier subs like the gen 2. Even with the gen 2 sub connected my whole lounge would vibrate and now with the gen 4 doesn't come nowhere near the loudness. The old playbar setup was a brilliant sounding piece of equipment with the sl ones and and gen 2 sub that used to be immensely louder and still had the clarity and performance as it is sonos after all. I can understand the new technology and trueplay taking acoustic environment into account, upward firing drivers for the 300s but the overall sound of the new system just sounds like it is underperforming. They are not building them like they used to. Happens In every industry. I wouldn't go recommending sonos to anyone after upgrading my system to only make me feel like I went backwards.
I have heard of others having challenges with their Sub 4 that it doesn't give enough bass, can't remember if there was a solution but you can try searching here in the forum.
I have absolutely no problems with my Sub 4, it is at least as powerful as Gen 2.
I honestly think you have a challenge because of something that is not optimal.
Maybe you should remove your Sub and add it again, or completely reset everything and start over.
true play actually turns the whole setup down. I'm familiar with the all the app functions and user settings Eq etc...just hasn't got that punch and loudness that the old system has.