I loved my 72cm mast but recently broke it and switched to 92cm.
It is correct that the shorter mast allows smaller shifts in rider weight to have more effect, so I would agree that it is less stable.
With the switch to 92 cm, I can actually notice that it takes slightly more effort to maneuver, but it's not a huge difference, and not that big of a deal, even though i was initially worried about the change.
You can see my concerns here; viewtopic.php?t=2417075
It took me one or two very short sessions to get used to the difference.
Having said that, I would prefer the 72 for small waves, as it is just a very slight bit more responsive, has less inertia, and it's just a bit quicker to turn.
In the interest of full disclosure, I switched from an old 72 Moses mast to a new Sabfoil 92 Sabfoil "surf" mast. So it is possible I am not comparing apples to apples.
I have in my possession a Slingshot 111 Ghost Whisper mast, which is identical weight as my 92 Sabfoil surf mast, but obviously not as stiff.
I haven't tried it yet, mainly because it's a bit of screw around to fit a board with a mast that long in my hatchback without disassembly, but the weight difference between the 111 and the 92 surf compared to the old 72, is... at least a pound?... I forget exactly, but aside from performance characteristics that some might not even notice, the weight difference is significant.
In the end, it's all going to come down to rider preference...
And just for example, when I ride a twin-tip I prefer a very fast board and a smaller kite,so that I can use speed to my advantage
Personally... I hate going slow.
On the other hand, I know plenty of people who prefer a draggy twin-tip board and the biggest kite they can possibly hold down, so that they have the best opportunity to use all that lift to their advantage...
It's all good!
Find out what you like!
Borrow your friend's gear every chance you get!
Hell. I'm happy to lend my gear out to people I barely know.
Kitesurfers tend to be cool that way, or at least, most are cool in real life...