(Personal opinion below, and does not necessarily represent the views of chess.com management or anyone else with authority or insight.)
1st, most people abide by Terms of Service - so, abuse of privilege is limited to a minority.
2nd, for those who choose to abuse the privilege here by multiple or serial accounts, there are consequences upon identification. Accounts are closed daily for abuse of privilege, I'm sure.
3rd, the pay versus perk cut-points are something that management always has to fret over when offering free services versus pay services. They put them where they think they should be, then they adjust them if the points turn out to be ill-chosen. I'm guessing the tournament play cut-points were well-thought out. I'm sure they'll be adjusted if they drive the wrong behavior.
Your points are well-made, of course. I'm just guessing that they've been carefully considered in advance by management.
I heard something about free members being limited to 2 tournaments per day or per week or something... is this the case? If so, is there anything stopping them from bypassing that max by making new accounts? If not, isn't it a bit silly to make that restriction at all since in essence the restriction doesn't really exist and anyone who wants to play more than their limit will have an obvious incentive to simply make a new account which would account for how many fresh unrated 1200 players there seems to be playing tournaments right now?
The way I see it, it undermines the rating system to tell players they can't play something without making a new (free) account. One solution would be to remove the restriction outright and let free players play as many tournaments as they want and another would be to not let them play any at all. The latter would really suck not only for free members but paying members though since before live tournaments were accessible to free users, it was often hard to get enough premium people to play one. I think the appeal of Chess.com would be much greater if everyone were allowed to play as many tournaments as they wanted to. Alternatively, letting free users play a very generous amount of tournaments (not unlimited but more than 2 per day) would be better.
If something is done to prevent individuals from making a hundred accounts to get around the limitation, my entire post can be disregarded. Maybe if 20 accounts are registered from one IP in 5 days it should be flagged but then could that not have some unwanted consequences for libraries, schools, internet cafes, etc.?
If there's a limitation and nothing is done to prevent people from circumventing it like that, I see that as a problem. If something is done to prevent it, I'm curious as to what rules come into play, how they are enforced and if there's any unintended consequences.