If HD weren't present then ppl would probably just complain about drive and ex combos, which do a heck of a lot of damage by themsleves, to the point where various characters don't need HD period. Might as well complain about neomaxes too, since they are so ultra like and a comeback mechanic.
At the end of the day SNK was smart in implementing HD, people love combos in fighting games these days and thats what the devs give them. BlazBlue, Tekken, Virtua Fighter, MVC3, Melty Blood, Guilty Gear etc. are all very combo heavy. Even Street Fighter X Tekken went the combo heavy route.
Yeah.. that's kind of the point
Don't know if its worth the meter to fish for throws and overheads at the cost of an entire HD gauge but whatever works.
Still the same mixup can apply with most of the cast though, since the vast majority of the time people turtle when they see an activation. Its not really Leona specific.