(Rosegarden is an incredibly nice and
professional-feeling program,
but for example, even the crap Voyetra sequencer that came with my
sound card back in 1995 let me select a group of notes and drag a
certain way to change their duration.)
It's not easy but it's not totally impossible: Select notes, then use the
resize tool to resize one of the notes and all others will follow.
I'd prefer keyboard modifiers with the select tool; Shift to resize, Alt
to move, Ctrl to delete for instance..
Tommi