Arnold is rather built for quality and robustness, than final speed. That’s why big studios like it and most of us don’t.
Things are changing, but only a year or two ago, Marcos Fajardo from Solid Angle was still very much against denoising and any shortcuts, while also skeptical about GPU rendering. It was all about “Brute force everything” and “Machine time is much less costly than human cost so just throw more CPU at it”.
I believe they’re pretty good at that, production proven, memory efficient etc…
But for most indies/small/medium studios it’s probably not the best option when you have renderers that just “Look good” (no matter how they cheat it) and get to the final frame much faster.
Oh and since Autodesk bought it and changed the licensing, it’s no longer available on some renderfams either (like Rebus).