I mean, 'not better than Doom 2016' is subjective. There are plenty of people who think it *is* better, and even if you're one of the people who think it's overall not better, you still have to admit that despite it potentially not being as good in some ways, there are still other ways that it is better. For example, load times are a fraction of what they were in 2016, and despite the overall graphical improvement, general performance has not suffered. If you have a GTX980Ti, you're not going to have any problems with running Eternal at all, it'll be silky, buttery smooth.
The gameplay loop is good, imo. It is a bit changed from Doom 2016, but not necessarily in ways that make it worse. I really think it just comes down to preference.