First of all, yes. I do think blackmailing someone else because you are pissed off is better than blackmailing someone for money. They're both selfish acts, but I still think blackmailing for cash is worse.

Why?

You seem to believe Irene Adler is somehow weak-willed or wishy-washy

No, I said "hypocritical", and I meant "hypocritical".

or after falling in love has the ability to realize when she's holding a grudge and when she needs to learn how to let go.

Or she realized she has as much to lose now as the King? I suppose her hubby might not care about the affair, but...