I have no idea what questionable deals Utd or Chelsea have done and I have no idea whether you'll be better off with Usmanov but ultimately the best you can hope for is spending all the money the club generates rather than that money sitting in the account.
They are allowed to spend the money in the account, if the owner wanted it, it wouldn't be in the account.
There are two things to consider, good business is not running a big loss, then there is what you can spend. We have a ~200mil a year wage bill, we make a small overall profit because of the high wage bill, so we may have another 200mil cash on hand to spend on new transfers but if we bought lets say 4 players for 50mil and they each wanted 150k a week that would add 30mil to the wage bill, which takes our yearly business from profit into a fairly large loss and then we have an issue in terms of long term health.
I've been saying it for a decade, Wenger CHOOSES to have a HUGE squad, pays way over the odds for the quality of players and then can't afford to spend more. Wenger this this is the way forward, Wenger doesn't run a club on a shoe string budget or do anything magic, he chooses to spend his money differently from most managers. Almost all other major teams including the likes of barcelona have smaller squads than Arsenal but far far more concentrated quality. Arsenal have 30+ players with 1 star, 4-5 good players, 23-24 mediocre players for the wages we offer. Barcelona have 5 stars, 10 great players, 5 average players and that is it.
WE cut some overhead but not enough, we also gave a huge wage to Kol and we've yet to see if that will pay off and we have offered a huge increase to Ozil. Arsenal needed to dump 15 players from the squad and bring in 4-5 stars, we had the money and the wage budget to do so. But we can't spend that 200mil without selling a huge portion of the squad to allow higher wages for a lower number of players.
I mean when I think back to someone like Bogarde, he was a waste and the club didn't renew his contract. Diaby can't play for years and was monumentally over hyped because he couldn't play, but he got multiple new deals despite being a clear as day waste of money. Rosicky to though a hugely better player he was both constantly injured and at times when fit he was being ignored anyway. Wenger even not using him gave him another new contract.
Wenger is 100% allowed to spend the bulk of that money but Wenger chooses to have the club in a position of a huge wage budget and huge squad which prevents bringing in more stars. New owner would only change that IF a new owner fired Wenger and insisted on a smaller higher quality squad though I'm fairly sure Usmanov likes Wenger too but thinks massive spending will help the club. In reality if he told Wenger to ignore the wage bill we'd start making huge losses after a couple of years of spending.