Even Microsoft with its infinite money failed when competing, because a monopoly to most of the Internet's email and video is just that powerful.
At least for the mail, that's perfectly fine. I could imagine that heavy users of YouTube don't like NewPipe, maybe? Works fine for me.
Really, the only thing is that I don't have Google Maps (but I love OSMAnd and Organic Maps). To me that's fine, but many people find it hard to move to OpenStreetMaps.
I have tried Cyanogen in the past, then Lineage, and always went back to the stock Android. I must say that /e/ OS is the very first one that I consider almost at the level (requires to accept NewPipe, K-9 and OSM, but no weird update flow or tuning or crashes or anything like that).
These days I’d also think the bigger question would be availability of popular streaming music & video apps and Tik Tok.