Apple’s Terminal.app is more performant rendering text and more responsive to input while admittedly having somewhat less unnecessary features.
In fact, iTerm is one of the slowest terminals out there!
See: https://danluu.com/term-latency/
iTerm used to have a lot of really compelling stuff that was missing from the official terminal like tabs, etc... that made straying away from the canonical terminal app worth it but most of them eventually made their way to Terminal.app so nowadays it’s mostly just fluff.