Attack Gamemode issues

Getting into the Champs with 115 is quite decent, but you need to keep in mind that the first week after the season reset is always the worst for the lower-tier players, as the majority of the upper tier does end up in the same pool in Legendary, like your screenshot shows (in the past, we were moved back to World Class). You have not been matched with people outside of the division/tier they were currently allocated to, so technically, until these players get promoted, they will be in the pool you could be matched up with, as per what seems to be the current design.

So you need to wait for them to be promoted, not to see them until you work your way up into Championship, which is a bit trickier because the P2Ws can't go higher, so if there is no one in their star tier, it will cascade down playing vs 117-119, who can't have a shot at as many stars as they do, so when it happens, you will match up vs 123s (ugh).

The matchmaking would be better if it kept it to -/+ 1 OVR, but it's not. I have seen a fair amount of feedback on the matter from both sides, also from P2Ws with 120+, complaining that basic chances often are good or great and the much lower OVRs score 10+ vs 123 OVR team. It's an ugly one and won't be easy to fix, but as I am told, it's being looked into (not having high hopes as this has been a problem for many, many years, although the current setup does seem to be more fair than the old fans count)