You are making excuses for what Anderson did, so that you can justify what followed as having the imprimatur of legitimacy.
Washington DC did not send him to Sumter. He decided to do that himself for tactical, not strategic reasons. The Fort was of no value to the Union other than as a bone of contention. It had no significant purpose to the defense of the Union.
"The plan succeeded. They attacked Sumter – it fell, and thus, did more service than it otherwise could."
No excuses. Anderson had the authority to move to Sumter.
His decision was a tactical decision to provide a more easily defended position then the open pit batteries at Fort Moultrie. Maybe Floyd should have ordered him out of Sumter.