The MaxEIRP is the regulatory max allowed (based on AP type, country code, if there is an external antenna and how it was provisioned, etc.
AP:HT:6/9/21 - This AP is running on Channel 6 (HT20), at 9dB EIRP, and the regulatory max for this AP/radio is 21dB (so if you set the ARM for 30 and manually set it for 30, it will only go up to 21 anyway)
AP:VHT:161/18/22 - This AP is running on Ch161 (VHT20)m at 18dB EIRP, with a regulatory max for this AP/radio is 22dB, so even if you set the max EIRP (in ARM or static) to 30dB, it will only go up to 22dB.
So you have the AP profile set to 15 (default), but ARM is set to let the AP run between 9dB and 18dB EIRP. So the AP is within your ARM range. If you disabled ARM, the AP would drop to 15dB EIRP. And if you set ARM to disable and set the AP profile EIRP to 127, it would max out at 21dB on the 2.4GHz radio and 22dB on the 5Ghz radio.
Why is the Max EIRP showing 21/22 and not 18? It always seem like the G radio takes the min tx and A takes the max tx when defined is there a reason for that?
In general, there are fewer 2.4Ghz channels (3 non-overlapping in US), which means there's far more ACI and CCI so the power range adjusts downward. On the 5Ghz side, there's FAR more channels, (esp if DFS is enabled) and as such there is FAR less ACI/CCI and the APs can run louder without interference.
Hope that helps.