OP seems to be using a MOLLE waist belt as an ALICE belly band.

Yes, that's apparent from the photos.  You might consider using the MOLLE waist belt as it was intended to be used--as a waist belt, instead of a belly band.  that way, it will take some of the weight of the pack, instead of all of it being on your shoulders.  To do so, I suggest raising the MOLLE shoulder strap assembly as high as practicable on the frame, and adjusting the shoulder straps accordingly.

You are correct.  In bygone days, the US military used to carry a lot of their Individual Fighting Load on their pistol belts, which had their separate harness.  The ALICE pack was originally designed to ride high to accommodate the IFL, as it was assumed the pack would be cached prior to combat, and (hopefully) recovered later. 

However, it was discovered (after a couple of decades of user complaints) that the ALICE pack, as originally configured without a load-bearing waistbelt, put entirely too much weight on the soldier's shoulders and forced him to lean far forward, which did nothing to enhance personal mobility, let alone situational awareness.

After a few false starts, the Mil decided that since the Soldier had to wear some sort of armor vest, that would be a good place to locate a lot of his gear, and his now much heavier pack, which screamed for a load-bearing waistbelt could be grudgingly be given the space around the soldier's waist to have such a belt.

The good news is that modern Soldiers don't walk arched-over while wearing a pack as though they are searching for gold nuggets in the soil.  The bad news is that the Mil has discovered that with modern packs with load-bearing waistbelts  they can further burden the Soldier with yet more stuff.

Your ALICE pack is fine for about 30 pounds or so, walking over uneven terrain.  Past that, weight limit (and experienced Soldiers will laugh themselves silly at such a low pack weight) you will come to hate, with the fire of a thousand burning suns, the designer of the kidney belt.  FWIW, the Civilian pack-toting people had discovered the load-bearing waistbelt long before the ALICE was adopted.

BTW, your ALICE should definitely include a sternum strap for increased user comfort.  Having such a strap, you will no longer need to have your hands more-or-less constantly re-adjusting your shoulder straps, and will have them free to do other things, like holding your rifle, or any thing you could imagine your hands doing. 

Now, with all due respect, and having used an identical rig a number of times, I suggest NOT spending another cent on improving it.  I have done so, during the time frame in the past when doing so seemed reasonable.  That time frame is long gone.  There are so many much better alternatives to the ALICE pack, particularly the framed, Medium ALICE pack, now available that no sensible person could, in good conscience, suggest a Medium ALICE, Mil-framed pack for anything but the most austere use.

If someone handed me a GI-framed, Medium ALICE pack, and said "raf, pack it up, and we're heading out." I would figure that either they hated me, or did not know what they were doing, gear-wise.  Maybe both.  If they handed me a Large ALICE, GI-framed pack, I'd know they were niuts.

OTOH, that identical frame, with a couple of ALICE Pack cargo shelfs, can be used to transport all sorts of things, like ammo cans and 5-gal cans.  You'll need some tie-down straps.  Image of ALICE Cargo Shelf:  https://www.amazon.com/Alice-Frame-Shelf-Cargo-Support/dp/B01HOXB1OO/ref=sr_1_1?ie=UTF8&qid=1486156563&sr=8-1&keywords=alice pack shelf.  The one pictured in the link provided is correct for the ALICE frame.  It slips over the horizontal cross-members of the ALICE frame.  Study the pic closely, and shop around.   The MOLLE Shoulder straps and waistbelt are excellent upgrades to a load-carrying ALICE frame with cargo shelfs. 

Sell-off the pack, upgrade the frame with MOLLE waist belt, shoulder straps, ALICe Cargo Sjelfs, and wrap-around QD straps, and you have something.  Buy another pack altogether.

Again, no offense intended, but I've BTDT, and I doubt anyone else that has BTDT would say much different.  Good luck! 

Allow me to suggest reading some the threads and posts by ROCK6, a member of this forum.  I consider him widely experienced, and well-informed.

I can say for certain what sucks, as I've done it.  ROCK6 is miles above me, and can tell you what is good.