Your KTM could work! ... and if you put in the amount of work modding your bike that RTW Paul has, then it may be reliable. .. or not. (I'm following Paul's report too ...followed him for a year when he was in South and Central America on his Tenere')

If you really learn your KTM, dissect it's many faults & foibles and work your way round them all ... then you've got a bike that is good! If you don't mind the Vibes on your KTM ... then all good. (owned two KTM 640's) If you're mechanically astute and have parts and tools ... then all good. Not a bike for amateurs.

I believe the KTM will require just about as much prep/mods as either
XR-L or DRZ400S. Parts? Just because a town in Honduras or Peru' has a Suzuki and Honda dealer DOES NOT mean that dealer will have parts on hand for your bike. They just won't! You will have to wait.

Same with KTM. Set up a deal with a good KTM dealer in USA ... one email and parts on their way to you. In the end, probably about the same or shorter wait as ordering from a local Honda or Suzuki dealer.

Can we assume you are US/Canadian citizen and starting in USA?

I'm not an XR-L fan. Bought one NEW in 1993. Sold it off in less than a year. The motor runs HOT. Sub frame bends/breaks. Battery box breaks off. All can be helped with good mods and aftermarket parts.

Like your KTM, the Honda is very tall ... but suspension needs help to be it's best, the rear shock is a POS. Ted says the XR-L is very popular in USA. I'd say "it used to be popular!" but not much now. I rarely see one anymore. Lots of Orange bikes here in California. Honda are OUT.

The DRZ has the off road advantage over the XR-L with a few key mods. If you can get a better seat and fit your luggage, it's not bad. I owned a DRZ400E ... only rode Baja on it with a small backpack. Never toured. But many DO tour on the DRZ-S. See Adam's Jedi reports on ADV Rider.

You say the XR-L and DRZ are "very similar bikes". Not at all similar. The XR-L is old school air cooled, radial valve head, NO oil cooler, CV carb. The DRZ is liquid cooled, much more modern chassis, stronger everywhere, better design overall. (stock vs. stock)

Both can be modified to be super good for travel, both will make it. Your idea of going light is very smart. 40 lbs. is perfect! I carry about 60 lbs. on my
DR650 and trying to cut that down some. (not so easy)

Best of luck. I'd take a few short-ish shake down rides locally to figure out what bike is best for you.