I do have a comfy seat on the drz and I have done 400 mile days with her. I have been pondering the 701 and so far it is my #1 choice.
As JT noted, I have a 701 Enduro.
I have modified it to be more comfortable on-pavement by adding a Seat Concepts seat and a
Madstad windscreen. I have lowered the suspension 1 inch to accommodate my inseam.
My experience with the 701 is vastly different from that suggested by focus frenzy. I do not find it to be too short, too light, or too twitchy for serious pavement or highway riding. In fact, in direct contrast, my 701 handles like a sport bike on pavement - fast, smooth, stable, and confidence inspiring. I routinely do 100+ mile pavement day rides in the hill country on it and would not hesitate to ride it at highway speeds all day long. A 30 mile commute would be of no concern at all. It is a joy to ride. I can only imagine the supermoto version would be even better on pavement.
As a point of comparison, I have owned two DRZs. One was unmodified and my experience was the same as yours - it is severely limited by the narrow ratio transmission.
The second DRZ I modified with a big bore kit and an
aftermarket wide ratio transmission from ACT. These two mods transformed the diminutive DRZ, making it much, much better on pavement versus a stock DRZ. It is the bike Suzuki should have been building all along, in my humble opinion. I ultimately sold the DRZ because it vibrated at a frequency that bothered me greatly and I couldn't find a windscreen that worked for me but those are idiosyncrasies specific to me.
As has been suggested previously, if you like the DRZ then you very well might be dissatisfied with the other heavier, slower, and less capable Japanese dual sport bikes.
If money is not the deciding factor, I recommend a 2017 or newer 701 (the 2017 701 got an upgraded motor - the 690 did not).
Otherwise a modified DRZ with a big bore kit and a wide ratio tranny would be my second choice for you.
Third would be a XR650L, another bike with which I am personally familiar. The XR-L actually performs surprisingly well on-pavement with its wide ratio 5 speed transmission. A fact that doesn't seem to be well known is that the XR-L tranny is
wider than the tranny on the KLR650. However, the XR-L does require at least one upgrade - at a minimum you will have to do something about its tendency to overheat at highway speeds, but that is typically addressed with a readily available aftermarket oil cooler.
Any of the three choices above would be, in my opinion, an improvement over a stock DRZ for pavement riding. For highway riding, the difference between the XR-L and a modified DRZ would be noticeable but not huge and would be about the same as the difference between a stock DRZ versus a modified DRZ. There is, however, a world of difference when stepping up to a 701, a difference that can't be properly conveyed via mere words on a forum. It can only be understood by riding one. I don't mean to imply some mystical quality to the 701 but the technology of the 701 is 20+ years newer than the DRZ or XRL and makes for a dramatic difference. Heck, 74 horsepower (701) versus 32 horsepower (DRZ) at the same weight (both bike are about 320 lbs) provides, all by itself, an enormous distinction between the two on both paper and in the actual riding experience.