That dealer guy who "giggled" and said it's a normal Jeep thing was just being an ignorant a**h***. In 20 years of Wrangler TJ ownership, I have only had fully developed DW once 17-18 years ago and a partial 'almost' DW several years ago.
Both times the root cause of the DW was imperfect tire balance. How susceptible to DW a Jeep is also depends on if there are worn parts that aren't able to dampen out DW before it happens. Loose/worn track bar mounts, shock mounts, control arms, etc. that can usually be spotted by the above recommended dry steering test.
First, I'd take the Jeep into a good tire shop and tell them you want them to spend the time to get the tires
perfectly balanced. Most shops only take the time to get them balanced 'good enough' which is not usually good enough for a vehicle that has a front-end like the TJ does... which is also common on Ford, Dodge, and Chevy pickup trucks that are also susceptible to DW. It could also be that there's simply a bad tire causing the DW that balancing won't help.
Before or after that, do this which is the dry steering test. With the tires on the ground and a helper in the driver's seat, have the helper repeatedly turn the steering wheel back & forth while you examine everything in the front-end while it's moving. Look for any side-to-side slop where anything is bolted together, look for unwanted movement anywhere between anything. Know ahead of time that the tie rod and drag link are mounted on ball joints so you will be able to rotate them back & forth on their ball joints. There should be absolutely ZERO side-to-side movement where the track bar is mounted, especially at its passenger-side mount. Look there especially while the helper is turning the steering back & forth.
Here's the front-end so you can identify the parts like the track bar...