They were fine, they are the least of this film problems. I actually really like Sersei, Makkari, and Ikaris as characters and I can take or leave Sprite. The Biggest issue for me though is Ajax.
Their story should have been told in chronological order from the past to present instead of skipping around. I would have appreciated their development way better. Some members I liked, and some I wont miss. But Eternals left alot of unfinished character arcs that I hope we get answers too.