Bit confused by all the 'PAPI motion', FD, and I think worrying about 'drag curves' just complicates the issue?, but in essence the slower the g/speed the less the required ROD for a GIVEN approach angle. The problem comes if you slow TOO LATE, and then, yes, the a/c will go higher on the approach, making the problem worse, whereas if you could slow earlier you have more time to lose the excess height, and of course, if you could slow to ZERO g/s (ie a Harrier) you would have forever to lose the height (until the fuel runs out or you get bored
)
The classic example is when descending near terrain where you wish to limit ROD to, say 3000fpm for GPWS protection, but you are high. 3000fpm at 300 kts will keep you high, but 3000fpm at 210 kts will give you more time to lose the height.
Is that what you asked?