The only thing that matters is did Manafort do the crimes. If you read the indictments, plural, it appears the money left a trail, the bank fraud left a trail, the tax fraud left a trail, and there is little to no guessing about what happened. Just on the bank fraud, he took financial statements that said his companies operated at a loss, converted them to Word, changed some numbers to add more than $3 million in income, converted them back to pdfs, and submitted those fraudulent statements to banks for loans. They have the emails from Manafort and Gates documenting this. Are you suggesting that's okee dokee and he shouldn't be prosecuted?
They'll have his tax returns. It's easy enough to see the income flowing to offshore accounts, then to his bank in the U.S or to lenders/sellers for property acquired in the U.S. and then to check and see if he properly reported that income on his returns when required.
The records I've seen indicate Manafort isn't rich, but loaded with debt, and no money coming in, with $millions on the way out in taxes, penalties, interest, fines, legal fees and more, which is why he had to try to offer up a house already pledged for ANOTHER loan as collateral for his bail application.
You're asserting things that the evidence contradicts.