Gotcha, yeah I haven't skied the Vacation but I've flexed it (the current 104mm-wide one) and its flex pattern isn't super far off from the Reckoner 112. The Reckoner's shovels might actually be a touch softer but it's stiffer around the bindings. Cy will be skiing the Reckoner next season so he'll be able to compare to the Vacation, but that won't be happening for a while, unfortunately.
Overall, I'm pretty confident the Reckoner will be less stable, mostly due to its more tapered shape and your note about the D'Sender's tail being stiff (the Reckoner's tail is not stiff). If you ski with a very neutral / centered stance, you can ski the Reckoner hard, it's just one of those skis where most of the stability is around the middle of the ski, rather than minimally tapered skis like the D'Sender where (I imagine) you can drive and engage the shovels.
FWIW, if you go to around 1:05 in
this video you can kinda see what I mean in terms of skiing style.