There are a couple of reasons the exhaust is hotter with our model sized 4strokes.

The 2stroke engines flow a bunch of fuel out the exhaust thanks to how long the intake and exhaust stay open. And some of that amount of unburned fuel comes from when the exhaust is open in the stroke. And since a 2stroke sees twice the number of firings, it's seeing more heat that needs to be exhausted, so the 2stroke designs consider that. So they usually pass through more fuel than less in order to carry off that "extra" heat. And the idea is that if the unburned fuel temp isn't somewhat cooler than hotter, there isn't enough being passed through so the designers tweak the timing to make sure they get that "cooler" exhaust. (A bunch of Control Line speed guys look at EGTemps. It tells them what their timing changes are doing, and when they've reached max or beyond.)

A 2stroke is also passing unburned fuel every time the exhaust port dumps into the muffler. And that unburned fuel is still cooling things as it goes out the muffler. It is actually carrying some raw alcohol that's still cooling things as well. A 4stroke only usually needs to dump exhaust into the muffler. And since the 4stroke has less combustion to cool in the cylinder, the cylinder fins wind up being "good enough" for the job, so it's exhaust doesn't have to carry out unburned fuel, so will actually wind up being hotter for that little detail.

And the timing on a 2stroke isn't controlled by a cam. It's more linear and because of that is less "accurate". When you run a 2stroke at less than it's optimum design rpm you wind up with a lot less efficient combustion. (Control Line stunt flyers discovered long ago that running their engines with a 2cycle/4cycle break would make them run LOTS cooler and last LOTS longer.) The cam on a 4cycle is profiled and can open at one rate and close at another.

The intake and exhaust timing for a 2cycle often has to be longer in order for the timing to work for all the functions the fuel charge does. You often have to have the exhaust open longer to help get the incoming charge into the cylinder. Sometimes the boost intakes, by their location, will spill undiluted fuel out the exhaust. With a 2cycle, you have the exhaust open while the piston is both going down and coming up. With a 4cycle, you open the exhaust only when you want and only for how long you want it and you don't have to have it open during compression or whatever...... So the 4cycle exhaust is really just exhaust.