Note input calls doLayout function (relayout entire score) instead of doLayoutRange, resulting in slow response time
So, the cat's out of the bag: "MuseScore 3 will be just as fast no matter how big your score is. " As explained in that blog post, where MuseScore 2 responds with a bit of delay because the entire score is laid out with every edit, MuseScore 3 only lays out the page(s) actually affected by the edit.
But, as Peter Jonas / shoogle noted , there are actually some types of (equally small and local) edits where MuseScore 3 remains just as slow as MuseScore 2—and it doesn't need to be. The most obvious one? Note input.
Take the test mentioned in that blog post, moving the first note in the Goldberg Variations. Select that note and use the up and down arrow keys, fast response time. But select that note and press a note on the keyboard... it's just as slow as MuseScore 2.
If I understand correctly, it's just a matter of calling a different layout function—should not be difficult to take care of.
Comments
See also https://musescore.org/en/node/115771:
"...note entry is often slower than note editing..."
Taken care of by Werner at some point in the past several months.