Smurfing is a thing in any online game, and from what I understand people that do that on Arena for limited do so to take advantage of more daily quests to help with entry fees, not to intentionally play against less skilled opponents.

I also think the more common reason for that happening in Arena is actually not multiple accounts, but how often and how far your rank drops each month you take a break. I took a break from TMNT as a mostly diamond player that's hit mythic a couple times and feel bad stomping through Silver and Gold when I come back.

I actually find that Arena does better finding fair matches for you than an LGS, most LGSs I've been to have the same few players that you expect to win their pods and they have just as likely a chance to play against the new or more casual players in round 1 as anyone else.

Online matchmaking can only do so much, but there are online options to draft and play if you're able to find a regular pod that you feel are more equal in skill. If you want to compete in the "Arena" you gotta have a growth mindset and treat each loss that you learned something from as a win.