The "high rate" thing references some old changes in filter ideas, that were mostly bogus at the time (30+ years ago).

The leaf problem points to something like the filter air vent. If there is an air vent, it should have a screen or something like it, on the upper exposed end. A small leaf could transit that tube, under certain conditions. Look at the part #12a in the image -- that's what WOULD keep out the leaf, if it were there.

Regarding the pump, depending on the particular pump model, it may be possible to replace the impeller / diffuser so that it will run as if it were a 1.5" HP pump -- the electric motor won't care, and your electrical costs will go down, while your filter efficiency goes up.

BUT . . . before you do that, you'll need to send photos to poolforum@gmail.com of the pump, filter AND piping. I'll post them, and we'll see what's possible.