the point here is: if your ordinary income tax is higher than your TMT tax, you can use your credit to reduce your ordinary income tax liability. That is AMT credit coming from. The logic beyond the practice is simple: let you use your favorable long term capital gain rate if possible.
But your case is bit different.
Even with cost adjustment, your TMT tax is higher than ordinary income tax, which means you have to apply TMT tax rate on your realized gains.
Something still confuses me. Why did you lose all credits if you still hold a portion of ISO?