Hi @Maxblender
Welcome to the Sonos Community!
There are a few settings which affect the bass level: Loudness, the Bass control and TruePlay. The first two of which are located in the EQ section of the Arc Ultra’s room settings (Sonos App » Settings » [room with Arc] » EQ). TruePlay can be found in the room settings.
I recommend as a starting point that you perform TruePlay Tuning. If you have an iOS device, full tuning will be available to you, which I recommend over Quick Tuning.
Your report surprises me, however - not only does Arc Ultra have the Sound Motion subwoofer driver, but it also has far more woofers than the Beam (Gen 2). It is possible that the Arc Ultra has an issue - a manufacturing defect - or that something has gone wrong with it’s configuration, somewhere. It is conceivable that a factory reset will help, but I recommend you first get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.
I hope this helps.