It's a forged knife, and the thickness at the handle is meaningless - it's an artifact of the process of making the knife. It has no effect on the geometry of the knife. Neither is the thickness of the spine by itself a good indicator of how a knife will perform. Of much more importance is the grind - is there a distal taper, how thin is the knife behind the edge, is the blade flat ground or convexed? I once had a custom chef's knife that was, for all intents and purposes, a flat plate of steel with no perceptible grind at all. It had a sub 3mm spine, so by your criteria, it should have performed well, but it was one of the worst performing knives I've had the misfortune to use.
Unfortunately, it is difficult to measure these things but easy to measure spine thickness, so spine thickness has become an easy way to compare knives, although not a very useful one, in my experience. The same thing happened with Rockwell hardness where it was widely held that the higher the HRc the better, but thankfully that has lost its popularity.
The worst part of all of this is that there is really no good way to evaluate a knife other than through someone else's opinion or by actually using the knife. My suggestion is to get to the point where you can participate in some of the passarounds that are offered at KKF so you can use a knife for a week and evaluate it. If you don't mind some additional expense, buy a knife, and if it doesn't meet your criteria, sell it on B/S/T - you will lose about 20% of what the knife cost new, but, as someone once remarked, you can look at that as the cost to "rent" the knife.
How truthful is that? Amazing thanks
From myself I could just add that even though you could buy a knife thinner from a custom maker it is very possible it will perform the actual cutting worse than thicker [theoreticaly] japanese knife