After all, a banking union implies a kind of insurance mechanism. And, as in every kind of insurance, only loss and damage that are not known in advance can be covered. For that reason, “legacy burdens” – in other words, those risks which arose under the responsibility of the national supervisory authorities – have to borne by the respective member states if need be.
Anything else would amount to a government transfer payment. Now, it may be that such transfer payments are considered desirable or even necessary. In that case, they should be made out of national budgets and with the approval of national parliaments and not under the guise of a banking union.