Could someone sufficiently motivated invest in training Katago to be able to beat Shin Jinseo with 3 stones of handicap? Unfortunately - probably yes.
This in no way detracts from how absurd and remarkable it is that Shin Jinseo can beat KataGo (it gets a LOT of training and architecture refinements https://katagotraining.org/#eloGraphButtons) with 2 stones of handicap.
Depends on where you put the perfect play ceiling. I think each side has good points in their respective favor. There have been strong pushes by both humans and computers in improving their best play in the past few years.
A 2 stone handicap, however, does not scale linearly with strength. It becomes relatively more impactful at higher levels. For pro players, 2 stones are gigantic, and for beginner players, they make zero difference. Same for a point advantage (komi adjustment). So there might come a point where it is physically impossible for a computer to beat a top human under some handicap.
This in no way detracts from how absurd and remarkable it is that Shin Jinseo can beat KataGo (it gets a LOT of training and architecture refinements https://katagotraining.org/#eloGraphButtons) with 2 stones of handicap.