I won't even try to be comprehensive here, nor do I know anything about pricing of either vehicle in your country, so this will just be my take on the major differences. I'm also not going to get into reliability, as it will take years for us to know as much about the Grenadier and QM as we do about the Jeep products.
QM advantages
1-
Much better drive train. The 3.6 Pentastar in the Gladiator is not very powerful, and the 3.0 Eco-Diesel has not been very reliable. The BMW engines are better, and the German-produced ZF transmission is probably better quality than the ZF in the Gladiator, which is made in either the US or Mexico (I forget which). Both BMW engines provide good low-end torque (much better than the 3.6). The 3.0 Eco-Diesel in the Gladiator also has excellent low-end torque, but seems to have over-heating issues when under significant load.
2- Stronger frame, axles, running gear (e.g. tie rod, track bar, drag link), and a stronger body with beefier good-sealing doors.
3- More comfortable seats (at least for most people)
4- Quieter on the highway
5- I think the QM has a better suspension, but the Rubicon and Mojave versions of the Gladiator are both pretty good
6- The QM has a fixed roof, which may or may not be regarded as an advantage. To me it is an advantage, as it is more secure, stiffer, quieter, and the roof is stronger (i.e. can bear a heavier load).
7- The 2.5:1 transfer case is
much better for dune bashing than the 4:1 transfer case in the Gladiator
Gladiator advantages
1- The 4:1 transfer case is
much better for rock-crawling than the 2.5:1 transfer case in the QM
2- The gear selector in the Gladiator is
much better for off-road driving than the BMW shifter in the QM
3- Some people love the removable roof panels - that's a personal preference (I prefer a fixed roof)
4- Easier to modify: (a) there are - as yet - no aftermarket gears for the Carraro axles in the QM, but you can get a tone of different gears for the Dana axles in the Gladiator, (b) multiple different lockers for Dana axles, (c) there must be close to a hundred companies making suspension lifts for the Gladiator, (d) you can get aftermarket tie-rods, drag links, track bars, etc. for the Gladiator, and lastly, (e) the Gladiator is basically engineered with the expectation that an owner will want larger tires.
5- Stock tires on a Rubicon or Mojave are 33-inches (stock on the QM are 31.6 inches - if it is the same as the Grenadier)
6- Disconnecting front sway bar (though it can have issues if repeatedly submerged)
7- The lockers engage and disengage better
8- Heated steering wheel as an option
9- Larger image for backup camera, and the backup camera comes on whenever you put the truck in reverse. The Grenadier's backup camera does not come on when the vehicle is in "off-road mode" - I would guess the same will be true in the QM.
10- If you buy one soon, the Gladiator won't
have ADAS (again, this is a personal preference, but I do not like ADAS - you might like it)
Conclusion: the QM has a better drive train and is built more stoutly. These are huge advantages over the Gladiator.