Some instruments are inherently more agile than others. Fiddles/violins have all the shapes closer together than, say, an acoustic guitar just because of the way they are constructed and tuned, and because of the differences in bowing vs picking. But of course a skilled player can outrun a half-fast player instrument for instrument. There are physical differences (air column length in wind instruments for example, and the mass of the sound-producing elements in others) that limit the speed you can practically change notes.
To give a more apples-to-pomegranates comparison, taking the skill factor out, compare the same guitar player on a dreadnought acoustic and a slinky electric, and they'll (usually) be faster on the more agile electric. Assuming the player is comfortable on both instruments to begin with.
For me, playing different keyboards with different actions gives a dramatic difference in the speed I can achieve. (Which is never much anyhow, but it makes the point.)
Anyway I think there is a reason the old composers gave the fast parts to the violins and flutes, and not to the tubas. :-)
-Glenn