I thought that NXT has been replaced by ARDOR and all devs have been migrating as well.

I used to have NXT, it was great tech, however I think they did not solve the "nothing at stake" isssue for their POS, I you try to corrupt the blockchain you are not risking your coin so even if the attacker has few chances to succeed he has no penalties to try, so over a long period it seems the blockchain is at risk.

With ethereum as you risk your coins you still have a few chances to corrupt the blockchain but block after block you are loosing a huge amount of coin, so it is an economical suicide to try to corrupt the blockchain.