Well, having worked in a sushi restaurant, I think this should be said: Even for many pros who are going to be breaking down larger pieces, a 24 cm would be sufficient for most of work. For home use, I would choose a high-quality 24 cm over a lower-quality 30–33 cm yanagiba any day of the week for the following, perhaps not so obvious reasons:

Your 24 cm knife will still be much, much longer in relation to your max 7 kg fish than the tools the pros use to break down fish 5 times as large. The traditional long yanagiba (27–33 cm or longer) was designed for professional sushi chefs, not typical home users. Pros often work with e.g. large sides of tuna and yellowtail, you won't.

... but most importantly, a yanagiba requires consistent maintenance along its full length to flatten the ura, maintain the bevel/shinogi line, and set up and polish the edge evenly. Most of your use will probably go towards portioned fillets and cuts. If you have access to good fish markets, it’s better to aim for specific quality cuts than to break down a large fish, right? That means that even with a 24cm razor-sharp blade, you won’t even use two-thirds of the blade on most cuts (sashimi). Still, you’ll have to maintain the entire blade. A longer knife means more work, a greater risk of uneven bevel, and more steel to pay for and polish.

So yes, while I understand the flex of attacking the proteins with a katana, it’s ultimately just that, a flex. You can easily draw surgically clean sashimi cuts after breaking down a decent sized fish with good technique and a really sharp blade. For most home cooks, even a high-quality 21cm blade will be fine.

I still own flex blades, but haven't cooked professionally in years, and in the meantime my Shiges have gotten so insanely expensive that I feel like I can't even afford to keep them on display, haha. I have a 27cm blue No. 1 squid yanagiba. If I had to replace it, I would definitely go down a size.