One key feature of the handling is the efficiency of the control surfaces (usually that's a combination of the rudder and, to a certain extent, the keel). It's not just a function of the size of the rudder, but it is connected to the drag that a large rudder vs. its ability to turn the boat. The deeper the keel, the shape of its foil, etc. aren't a simple design issue.

The balance of the sail plan vs. the ability of the control surfaces to overcome these is also an issue.

On our Pearson 35, years ago, if you had a large genoa up and a full main, close hauled in close to over-powered conditions you could effectively have a very hard time turning the boat without easing one of the sails. The boat was "locked-in" because the sails were steering the boat. I had that to much lesser extent on our subsequent Sabre 42 -- but it still could be "grooved" in.

Our J/boat has a very deep and much more efficient rudder (the bottom of the rudder is about 6.5' below the normal waterline with the fin keel being about 7.3' down.

The ability to turn a circle (under sail or power) is impacted somewhat differently under power then sail -- and different in various sea states and speeds.

I think there are a lot of factors that affect comfort, nimbleness (ability to steer easily and accelerate relatively quickly in light air), etc. are all features that are "un tubby" boats tend to display.

Where are you generally sailing, whether you like to be changing-up head sails, using a spinnaker, what length boat, how many crew and what accommodations you "need" below make a huge difference. If you can speak to that, you can get suggestions that are more meaningful.

Your framework of experience, expectation, and so forth makes a huge difference in how you define tubby.