credit in this game is not based on your past payments but on your cash, company value and profit position only.
No. This is wrong. Loans are based on your company value, age of airline, how much you already loaned AND if you can pay the previous loans, (it usually comes in a batch with the other costs).
So if you pay up all your loan payments without missing any single one (enough to pay on Tuesday or Wednesday), you get a good airline rating eventually.