Anvirol, you get what you pay for, and with a heavy laptop the shoulder strap / foam / stitches are the first to go.
As you found, the cheaper backpacks don't have much if any padding - you could get a slipcase / sleeve with padding to put around the laptop to help with the padding, but the shape of the G750 doesn't make it likely you will find one that fits.
I went through several backpacks when I had my Asus W90Vp-X1 18" laptop, and the only backpack I found that it fit, provided drop protection, and had room to carry other stuff was the Oakley Kitchen Sink backpack. At the time it cost $300, now it is down to $200 (yeah, I know, real money), but it is still in like new shape after 3 years + usage (I use other laptops/bags as well).
There are now many finishes and colors, and a "dress" version for $250. The default color is Stealth Gray for this link, but I have the original Black/Red/Silver theme (Black):
http://www.oakley.com/products/kitchen-sink-backpack/92060-013The Designer / Dress bag looks like it is covered in soft leather, not sure about durability, but it is Oakley so it is probably fine:
http://www.oakley.com/products/designer-bathroom-sink-backpack/92523-001Oakley has a lot of laptop bags:
http://www.oakley.com/store/products/men/bags-and-packs/computerSome bags might fit the G750, but when I went in to the Oakley store with the W90 the Kitchen Sink was the only one that worked - also - the W90/G750 didn't/doesn't fit in the laptop fitted area - the laptops fit in the larger area in front of the laptop area - I put my Macbook 17" in the laptop fitted area and the W90 in front of it.
The Power Supply/cables fit in the 2 hip zippered pouches, and all the other stuff fits in the top and 2 front areas. It is a bit over engineered - in that you have to release 2 latches to get to hidden areas, but you get used to it. There are internal zippered areas for small items, cables, pens, etc. There is a top zippered hardshell area where I keep my sunglasses and other stuff I need quick access to.
Very happy with the KItchen Sink backpack, and even though it isn't inexpensive, it is still going strong, and not showing any damage after ~4-5 years.