I don't think NASA really wants to give the benefit of the doubt to SLS. It's a congressionally mandated program, that NASA regularly proposes reducing the budget and responsibility for (e.g. https://spacenews.com/nasa-budget-proposal-targets-sls/), and Congress regularly rebuffs them and demands SLS.

If Congress passes a budget with $7B in funding specifically for SLS, you can't really blame NASA for spending that money on SLS.