Sorry for being imprecise. I didn't mean the J 109 was literally the J 105 hull with a cruising interior, but that complaints about the lack of a cruising interior in the J 105 lead J Boats to come up with the J 109 - i.e., a 35-foot sprit boat (like the J 105) but with a sensible cruising interior and some other improvements.
But, as you've been pointing out with respect to the A35 and similar performance cruisers influenced by trends in shorthanded offshore ocean racing, the J 109 remains within the more traditional design mode by not extending beam aft and broadening the transom and cockpit areas. I think that's what makes it feel like a smaller, more cramped boat (when the transom box is installed).
I personally prefer the more contemporary, beamier designs, with twin rudders and hard chines carried from amidships aft to the transom. Also prefer open transom and tiller / twin wheels to the single massive "destroyer" wheel of the J 109, which pretty much blocks access to the back of the boat, creating a less-than-optimal cruising experience (an issue with the J 105, as well, but not as big a deal for the 109 or 105 in closed-transom configuration).
What I do like about the J 109, as a singlehanded boat, is that it is very stiff and sails brilliantly upwind (though you need to install some kind of in-hauler arrangement to really adjust the headsail slot). I think the interior space is perfect for one person and totally like the aft head configuration. And, of course, there's J Boat France's repuation for build quality and strength. J 109s have done most of the major offshore races, under all kinds of conditions, and have proven bullet-proof. I wouldn't hesitate to circumnavigate in one, but only solo.