There's a limit to how thin even Japanese thin knives get. A super thin knife can make a little bit of difference with a few foods, but sharpness and technique are typically more significant limiting factors.
I have a couple of Thiers Issard "Nogent" carbon Sabatiers which are as thin as just about any Japanese made knife other than a Tadatsuna or the equivalent Suisun, I don't think I slice thinner with either of these than with my K-Sab au carbone, or "Canadian" Sabatier 10" chef's knives -- which are a bit thicker than the Nogents, but significantly thinner than a typical German chef's.
FWIW, stamped knives are usually thinner than forged, and if they're made from a decent alloy (Forschner Fibrox and Rosewood are made from the same X50CrMoV15 as most high end Germans), will have better edge characteristics if only by virtue of their thinner geometry.
For making thin slices, most (but not all) cutters do best with the offhand in the "claw" position using their fingernails as width gauge and their knuckle bones as a knife guide. You have to place the knife in the right place to make a good cut.
Then, the big deal is to have a knife that's sharp enough to cut cleanly at the first touch so as not to smoosh the tomato or otherwise distort it; and which is also thinned well enough (a part of sharpening) so as not to "wedge." Either will make you cut thicker.
One of the biggest things which makes the super thin Japanese knives so great is their ability to take an edge, and how sharp they act even after they're actually starting to wear. But, as to specifically cutting thin tomato slices, technique, sharpness, and an appropriately thin or thinned knife matter more than what knife guys call "Kate Moss" thinness.
Hope this helps,