Originally Posted by rowuk

The ease of bending depends on the "slotting" capabilities of the mouthpiece/horn combination. The better the mouthpiece/horn slots, the harder it is to bend. You will find horns in every price and weight class that are or aren't easy.
Why not just have horns built one way or the other?
My experience is that the trumpets that "slot" extemely well, do not have as broad of a palette of "colors of sound" as instruments that have broader slots but are easier to play. The broad slot brings a requirement for a stable embouchure and good ears for intonation with the advantage of more colors.
Before a bunch of you pile on and claim that your superior slotting instrument XYZ has sounds from smoky to glass cutting, let me say, check the math!
A slot can be defined as the intensity and width of a resonant tone. In acoustics we define this with the variable Q. The more resonant a particular tone is, the higher the Q. Our problem with trumpets is that we need more than one note, they need to be in "tune" AND of fairly consistent volume throughout all of the registers. Those factors cannot be easily balanced.
The partial series of brass instruments is not particularly "cooperative" and has led to the development of various leadpipe structures, mouthpiece backbores and throats, weighted valve caps, mouthpiece gap and tons of other things that in the proper dosage can get high quality results.
I say, generally a weaker embouchure needs a slottier instrument. A strong embouchure can benefit from a somewhat lower Q with the ability to bend pitch AND tone for greater musical effect. The higher the Q, the more the trumpet has to say about intonation and tone.
It is possible within certain boundaries to alter the pitch, width and the height of the resonance individually and that is the secret of the top manufacturers. They adjust their horns before (by design), during and after assembly to get the client the best match. That has nothing to do with bore, weight or other single factor. It is the intelligent combination of many factors for an optimal product which also includes the player.