There is a difference between 1 and 2.
1. Lords, of their own volition, joining a neighboring realm when their realm is collapsing to retain their lordship. That has happened throughout BM history and should continue.
2. Lords, under influence by their rulers, joining a neighboring realm to give a less hated realm more regions and prevent the more hated realm from conquering them. Especially when the rulers of both realms coordinated such a move with specific terms for those regions.
This is the crucial difference.
If the ruler of Terran was still railing against his cowardly lords who abandoned the realm in its time of direst need, there would be no case here.
But he's the one who was
planning this. That is what makes it a realm merger. Not the fact that lords happen to have taken their regions from a dying realm to a (more or less) neutral third party.
