I can't remember the last time I visited a Kubota dealer and saw a G series in stock--they have Ts, GRs, and then BXs. I'll be amazed if Kubota doesn't drop the G series at whatever point they consider it aged out. I'd like to see the sales charts, but I expect Kubota sells far more BXs than G series and JD likely sells significantly more 2305s than X700 series GTs.
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Keller Bros Kubota in Shaefferstown, PA had a
G2160 in the showroom last time I was there (along side a
GR2110). The
G2160 does seem redundant, to say a
BX1860 (and has less capability and features). I don't know if the
G2160 has available 4WS or not, but my
G1800-S has 4WS, which makes it much suitable for my mowing property than a BX. The
GR2110 would also be good for mowing my property -- again because of the tight turning capability. The
GR2110 is also AWD, which would make it better for my hills than either the
G2160 or my
G1800-S.
If 4WS isn't available on the
G2160, then it does seem silly to keep it around. Also, I don't know what the available PTO on the
G2160 is like, but on its predecessor, the
G1800/
G1900/
G2000, it was a proprietary 2000 RPM PTO, requiring proprietary implements. If you want to run PTO equipment, the BX is much better in that regard. JD got that one right with the 425/445/455, and also the X700 (and I assume X500, if they have an available PTO), as they used the standard 6-spline 540 RPM PTO.
As for the ROPS on GT's, JD integrates a ROPs in to the FEL for the X-series. A co-working of mine has an X585 with the JD FEL on it, and it has two square tubes sticking up in the air that serve as a ROPS. Of course, the fool cut them off

so that he could fit it into his enclosed trailers. He's already had one close call with nearly tipping it over.
This particular X-series owner chose it over the JD's SCUT (I think 2205 at the time), because it had cruise control, and other "creature comforts" that the 2205 didn't have. It actually cost more than a 2205, and had less (PTO is standard on the 2205). It is also a gasser, where the 2205 is diesel. I don't understand while anyone would go X-series over the JD SCUT (or G-series vs BX), except to get features that aren't available in the SCUT (the X500 and X700 series both have models with 4WS).
All these compromises are reasons that I have a G-series for mowing, and a B-series for everything else.