A poor flush is usually a function of the design of the route by which the waste exits the bowl, and, to some extent, the route that the water takes through the bowl.
As to the Europeans...nope -- it's not that they use more water. In fact, "more water" would seem to be a panacea for all poor flushes, but I am here to tell you that it isn't. You can empty three times the usual amount of flush water into a crappy low-flow and it isn't going to keep the waste from clogging it. On the other hand, Toto was able to reduce the amount of water through some of its floor standing models from 1.6 to 1.28 gallons per flush, and still have a greater than 1000 MAP score, because the design of the trapway was so ingenious.
My worst toilet ever was a gorgeous Kohler Portait low-flow with the "ingenium" flush that matched the beautiful sink we installed in the same room. After a couple of years of clogging on absurdly-low amounts of solid material, I hit it with a sledgehammer (happiest moment in a long time) and replaced it with a Toto Drake. It was the design, pure and simple, that was the problem, and I am still amazed that Kohler had the audacity to sell it. It was beyond terrible. (I don't know how the current version of this toilet compares; they may have improved it. Or not.)
One thought -- something doesn't have to be in a "suite" to be complementary in design. Just because the manufacturer thinks that one thing "goes with" the other doesn't mean that nothing else does. Get your Starck bidet if you want, and match it to either one of the Toto wall-hungs, and you should be happy both with the look and the performance. My Toto goes very nicely with the Kohler Portrait sink. Oddly, nobody has noticed that the toilet looks different; they only notice that the toilet works -- I usually get told by folks who had used the old toilet, "Oh, you fixed the toilet in there." (embarrassing to see how many noticed how poorly it flushed) They don't notice the fact that the two items don't "match".