Its a necessary evil unfortunately, hand drawing all this detailed action is not practical at all, the only example of that I can think of is AKIRA (and well.. it is one of a kind for a reason)
Incoming anime nerd rant I want to get off my chest. I swear this isn't directed AT you in a negative way. More just what I'd like to say to the millions of people making comments like this to anyone criticizing the animation.
I find this type of comment very interesting. It seems to be the most common response to people that complain about the CG integration in this show and I think really speaks to peoples acceptance and the normalization of CG in anime. It isn't necessary at all, as it is completely down to the director and production staffs decisions.
Mappa is a huge studio with the biggest names in anime currently under their belts such as Attack on Titan and Jujutsu Kaisen. They definitely have the money and capabilities to hand draw the show if it is what they truly wanted to do, but are taking shortcuts and are trying to elevate their CGI game in order to maximize efficiency and pump out more product. Hell, Attack on Titan had stunning hand drawn animation and hand drawn titans battling each other as well as humans in all sorts of creative, sakuga filled scenes, some that were quite revolutionary. Then the show gets picked up by Mappa and they change the titans to CG models and lower the overall animation quality. Was this a "necessary evil"? The show was clearly capable of high quality hand drawn animation with some animation cuts being helmed as some of the best in modern anime. Now, in order to be "practical" and pump out more series, the product suffers.
Also, CGI PERIOD in anime isn't necessarily the problem, but the integration of it. Some scenes in Chainsaw Man look fine, but to have some of those scenes (in the first episode no less) with the camera just lingering on a pretty poor model mostly standing around just look bad and detract from the overall quality of the show. If a character is just standing there, literally not moving at all, why is a not-so-great CG model necessary? In the third episode with the Bat Devil, there is pretty egregious animation error where when the model is talking, there is a doubled up lower jaw. It might sound like I'm being super nit picky but I really feel like I'm just being reasonable in my critique. I still like the show!
Lastly...and I promise I'm not ranting AT you...just being triggered by the comment. There are loads of examples of recent anime that have detailed hand drawn action animation, or at least of a much higher quality than Chainsaw Man. I'm a bit confused, are you saying that AKIRA is the only anime with highly detailed hand drawn action animation? Or are you comparing AKIRA's action animation to Chainsaw Man (in which case we might have a problem XD). Stuff like Kimetsu no Yaiba, One Punch Man, MOB Psycho 100, even MAPPA's own Jujutsu Kaisen have higher quality 2D action animation than Chainsaw Man. I just feel like with the hype surrounding this series and the inevitable piles of money this thing is going to make, they made a real gamble on the CG integration and I'm not sure if it's paying off for them. People will still love the series, and other will like it fine like myself, but they had an easy win on their hands with this one and have created what I think was an avoidable "controversy" around how it is being directed and animated.
The anime sure is horny, but in a funny/innocent sense, so to say.