I don't see parachuting as a replacement for a heavy VTOL combat transport.
For one thing, the infantry once dropped has no fire support, unlike a gunship/transport hybrid which can at least provide some cover. Even APCs would be potentially ruinous if the opposition is competent, worse if they have hovercraft transports with infernos loaded...with even basic gunship available the enemy has less time to contest and needs heavier response to dislodge troops. Plus, the extra mobility means that if your infantry needs evac or is needed elsewhere, they don't have to huff it on foot or wait for ground vehicles.
The second issue is attrition. You can pretty much expect between two to ten percent in parachute jump injuries, per jump with a combat load. Concussions, ankle fractures and sprains and so on. (Based on various studies and combat drops) Training jumps have about two percent injury rate, in comparison. This is with relatively modern equipment.
Paradrops can also go really, really badly.
During Operation Just Cause (Invasion of Panama '89) Rangers, who can be assumed to be well trained, in full combat load and night took fifty percent injuries from dropping. This was landing on an airfield, so hard surface, which is supposedly worse than sand. Now to be fair, lot of those injuries would not be severe, but that means that even with one in five injuries being severe you have hundred out of your potential thousand plus if you get unlucky if we assume a battalion sized drop.
Even '91 Al Salem, Kuwait combat drop had fifteen percent injured. Again, hard surface, night drop.
Basically: combat loads, night drops, high winds, hot temperatures, concrete and substantial humidity are bad for parachutists. So for planets with high wind, high humidity and high heat, parachutes at least aren't ideal.
No idea on what the injury rate on a jump infantry drop is though.
