Not these days. Native Compilation made emacs a faster and there have been a lot of other changes. In fundamental-mode, emacs can handle really large files. When opening files literally, it's even faster. I have this 104k line org-mode file and it's reasonably responsive. Reverting it takes a while, but the UI does not hang while the buffer is being formatted according to the mode.

I use a mid tier laptop CPU (6C12T). Emacs is snappy. Compared to what it's like now, it was glacial in 2019.