It's all about the onboard service level in JL F, and of course they are extremely good at that. But the seat is quite outdated and tired, zero privacy. The adjustments seem to be getting worn out pretty badly now as well, I've had a lot of experience in that seat, both on long haul F tickets and intra-Asia on C tickets when Emerald members could select them as a business class seat. You have to really coax the seat to move around sometimes, trying back and forth multiple times while the bottom gets caught up in the tracks.

JL's F lounge never was what I'd call a premium F lounge like CX, QR, LH, etc. but is even less so post-pandemic. Lounge food selection is mostly very nice Japanese, but there's not a very wide variety nor much in terms of western tastes. Pre-pandemic there were always bottles of Yamazaki 18 sitting around for self pour, these days there are a couple of nice aged Scotches but no premium Japanese whiskey in the lounge anymore. I don't know if the JAL's Salon have re-opened or not, they weren't being used last time I departed NRT and HND but that was Q3 and Q4 last year, that would make a night and day difference in the perception for those who want a premium drink, I'll be at the HND one next Thursday so will see. If JAL's Salon is still closed, I actually prefer CX's business lounge over JL's F lounge at HND now that CX is open again.

Onboard, again, service is top notch as is their Japanese whiskey (always something pretty premium available) and Sake selection. Seems the OP is interested in Salon (champaign) which is definitely very nice as well. I'm not a fan of their F menu onboard, but most other people seem to be quite pleased with it, so will rate that good as well.

Finally, JL's F ground service is zero if that's something you are interested in. No premium check in area, no escorts at any point, no being driven to the plane in a Porsche, etc.

I'm not saying they have a 'bad' F product, just it's not nearly as premium as I think a lot of people have in their imagination if they've never experienced it before. QR's Q-Suite (business class) experience tops JL's F experience in my opinion.