Oh trust me : The O.I. faithful have that angle covered as well. When you try to point out this line-of-reasoning that you cite, they will come up with elaborate pushback , of methods where it *could* conceivably have been done.
Like they'll point out that Cornish miners , in the middle-ages, dug elaborate tunnels into bedrock in European hard-rock mining, that did indeed have tunnels that reach this deep, blah blah blah.
Or they'll say something like : "Well gee, the pyramids of Egypt were built with manual labor, right ?" Hence if you get 100 men, for 100 yrs, then it can be done with pick & shovel. Eh ?
In other words, they think that if they can find ANY remote conceivable far-fetched way it *
could* have been done, then presto: They think they've proven that there's a "fabulous treasure" there.