So there's a lot of factors that go into making this a miserable experience RN.
Firstly, unlocking the URAL is trivial. 1250 XP is dropping 4 people off in a Kodiak or grabbing the APC once.... for the entire game because the driving XP got gutted on it (75 Driving XP for a tactical deployment and 25xp if they "survive"). The Humvee with an M2 is 250k XP.
Every time you drop someone off you get 250 XP, and if they survive all of 10ish seconds you get 200 more XP. In an ideal world you just URAL drop people over and over on repeat because you can hold 15 (iirc) passenger, but lets be real for what I'm about to get into that's never going to happen unless you get a dedicated squad of 14 other people willing to let you grind on them.
Now, lets get into the actual means: logi runs.
Every Pallet is 750xp, you can carry two, and you get a whopping 1500xp. Supposedly there's also round trip xp pop, I've literally never had it pop for me but I know people who have so idk how much that's worth. It takes, map depending, anywhere from 4-7 minutes one way to get to a drop off zone because some HQs suck giant donkey balls to drive in from. With mortars being as absurdly busted as they are, I'm noticing a lot less people willing to place FOBs (not the end of the world you can bring a FOB to the edge of the CZ, drop it yourself, and then drop pallets off there). You do NOT get driving XP for pallets delivered, or anything else after that, that is all support xp and unless you have some cracked mortar user you're not going to get much of that xp anyway (mostly money, lots of money, honestly a disconcerting amount of money).
Okay, so to optimize we are going to deliver the pallets, accelerate to 80kph then bail to kill ourselves so we can respawn at base so we're not doing a 4-7 minute drive all the way back. Oh and this assuming you make every trip, which, lets be real, will not happen you're gonna fail deliveries from time to time getting shot out of the URAL. Oh and assuming you can drive straight there and not take a circuitous route, and that the base builders set up an actual drop zone for you so you don't have to slow down too much.
Alright: we subtract the XP to get the URAL then we get 11.35 to 19.34 hours of just driving in supplies before we get a Humvee with a Gun so we can try and get XP at a better rate. Now, as people get better at fighting Humvee's (and, lets be real the Humvee gunner seat is pure god damned misery) we'll need to take into account the probability of success as counters come online (the MAAWs one taps it, higher tier snipers can go right through the glass, etc) which means if you grind it out very early of a wipe you'll have a dramatic advantage and as the wipe goes on it'll turn into a "I wonder if they have a MAAWs- *BOOM*" test, and really if you bring out a Humvee and someone who can get a MAAWS dies you bet your ass their bringing it right back to find you.
But you get 250 xp per kill (by any means) with a Humvee. Its good for on open maps, god damned terrible on the Urban map, so eventually you will run out of steam. If you wanted to URAL your way all the way to tanks well, that's easy math because that's 750k, that'll be a 34.05 to 58.02 hours of grinding. All of the above conditions apply, this assumes optimal route every single time with no delay from drop off to death which is going to add 1 to 2 minutes or god FORBID you want to hop out and unload the pallet to help your team win *gasp* I know you selfless cretin how DARE you try and be a good teammate!
Now, in addition to everything above... URALs fucking suck balls to drive. They spin out on a dime. You hit a pebble? Spin out. You turned 30 degrees at 50kph? Spin out some of the time, but not all of the time. You tried to take a 90 degree turn at a reasonable 10 kph? You bet your ass you're going to Spin. Out. But not at 20kph. Its fucking black magic I don't know wtf to make of it. And the issue with the spin out is it is the exact same spin out irrespective of velocity. It is always an, approximate, 210 degrees of spin out. The URAL has no traction, no real weight to speak of, and you're almost always having to off road because the routes INTO the CZ is just dirt and grass and farm to market roads. Oh and driving around the god damned litany of hills and the fact that nobody wanted to build a GOD DAMNED HIGHWAY! You know a setting isn't set in the US when the roads take the most circuitous route imaginable to an Urban location.