Tongue weight is applied by the trailer and will be the same regardless of how level the truck is. Leveling just ensures the weight is distributed between the axles and not maxing out one of your GAWRs
I may not be following your question fully, be ause you ask about tongue weight being the same but the title is about air bags vs WD and leveling effects.
Hopefully this helps. The tongue weight is the amount of weight applied by the tongue of the camper (and many say any cargo behind the rear axle in the bed, but that's another conversation). Weight distributing hitches or air bags will not change the tongue weight that is applied to the truck overall. However, both options will level the truck and by making the truck level the tongue weight will be distributed across both axles instead of only the rear axle.
Technically speaking, if the truck is sitting level, then weight distributing hitches are not needed. However, there are added sway control benefits with some of them that make them worth it even with air bags.
I don’t 100% understand your question, however I might just chime in. A few years ago a family member waisted a bunch of Money on a brand new 32’ camper 6500 lbs with a WD hutch set up. It was set up from the dealer ship to work on another family members 2500. When I went to hook up to it before a camping trip with my wife and kids I noticed significant sag even with the WD hitch. I bought a set of air lift 1000 which in my head was going give me the same rear suspension set up as the 2500. And it definitely helped the sag and made everything very level. I Pulled the camper roughly 2.5 hours away with my 2011 1500 other than terrible mpg and not setting any land speed records it did just fine.
Your assumption is correct. Airbags can lift the rear to level the truck but it will do nothing to distribute tongue weight. Using a WD hitch acts like a lever which will lift the rear of the tow vehicle and transfer weight to the front. The tongue weight doesn't change, only where it is being applied does.
For example, a trailer with 1k tongue weight on a regular hitch applies the full 1k on the rear axle. This will sag the rear and lift weight off the front axle. Using airbags can raise the rear height but does nothing with the weight.
A WD hitch when properly set up will transfer approximately 20% of the tongue weight to the front axle and another 20% back onto the trailer axles leaving the rear axle carrying 60%. The truck would carry 800lbs of the original 1k still but only 600lbs on the rear axle as opposed to the full 1k. Of course results will vary by set up.