^Sprite used the Uni-Mind and the power of the dreaming Celestial to warp reality and erase Eternals out of existence. They were stripped of their powers and memories. Ikaris was the closest to regaining them but was damaged and needed repairing.
https://readcomiconline.to/Comic/Eternals-2006
Even in that weakened state, he was nearly impossible to kill. When he was fully revived he was back at full power, he could fly, control minds, had telekinesis, teleporation etc. It's hard to imagine how Marvel won't have to downgrade the Eternals. They all have things they're adept with but each has a baseline set of powers like the Martian Manhunter outside of intangibility with various specializations.
P.S. That grenade was deviant tech I believe. They ruled most of the world a few million years ago and were way more advanced than humans back then.