It's potentially an "attack". If the idea is to transfer stake from one chain to another and utilize dominant stake to "encourage" the transfer, then it's an attack. It does not matter the intention of the party attacking the chain, even if is it supposedly to everyone's benefit (in the long run, it typically isn't). The way witnesses have been elected is notably very weak to such potential attacks and we'll see what happens. But in a real blockchain, no party is obligated to move their stake to another chain. If that happens, the chain never had any real validity to its claims of censorship resistance or decentralization it initially claimed in the first place.

But if this is an overreaction, consider a government or large corporation doing the same thing. Because they just as easily could. The fact that such a transfer is possible should be gravely concerning to anyone who believes in decentralization, because this move is simply a move that continues a trend in society towards centralization. In the long run in the centralized game, only those with power and money win.