If you have the right tires you won't get flats from goatheads, I know this because I use to live in the Mojave Desert of California. The only tire I found back then that worked, after trying many tires, was the Specialize All Condition Pro, never had a flat with those, but since that time a few other tires have come along that would be virtually flat free as well. You may have had a lot of flats with goatheads, I don't doubt that, but the blame for those flats was your tires that were not up to the task. I've done some loaded camping and with Schwalbe Marathon Almotion tires, which are not supposedly as good against flats as the Marathon HS 440, but I haven't had one flat yet. I opted for a lighter tire knowing I was raising the risk of getting flats, but I don't want to be touring on 960 gram tires, the Almotions are around 625 grams and have a lot less rolling resistance than the HS 440's.
Your experiment was flawed, the tire is a sealed tire, there is no place for the liquid to evaporate away like with the paper towel thing you did. On top of that, a small pin hole prick would probably only leak out maybe a gram or two at the most, so you would have to have a lot of pin prick holes to lose 3 or so ounces of sealant, and no one gets that many holes. The sealant will dry out inside the tire, but what state does it leave when it dries out? sticky patches, and or dried CLUMPS of cured latex, the stuff is still in the tire, it just turned into another state.
At the end of the day you have to do what you think is right for you, for me, I don't want to deal with trying to reseat a tire on the road because you can't so I have to carry a spare tube or two, I have to do that anyways whether it's tube or tubeless. And with using the right tires flats would not be all that common if at all. Of course, the argument would be that using the right tire you wouldn't get any flats in a tubeless either, and that's true! But if you do have one, it's more of a headache with a tubeless set up.
Another disadvantage that I forgot to mention is that the sealant is known for clogging valves.
I think the weight thing is false between the two types, by the time you add in sealant, special rim tape which is heavier than standard tape, you're pretty much a wash.
Running lower PSI using tubeless increases the chances of damaging the rim.
Removing a tubeless tire after the sealant has dried will leave you with a sailor's mouth, although if you use a C clamp you can break the seal easily enough.