thats merely a circulated myth that got alot of momentum. especialy considering mealworms are a staple diet
you have to consider that there are a great many insects with chitin that they would gobble right up.

mealworms are just fine, i assure you. they are the main diet to my own leopard gecko colony even. ill even take a quote out of a book written by one of the most reputable breeders in the leo community. ron tremper.

"mealworms, once the staple for keeping insect-eating lizards, have unjustifiably gotten a bad rap in recent years. unfortunately, many myths are still circulating in the reptile hobbyist community about mealworms, including that their chininous exoskeleton cannot be digested and therefore can lead to impaction, and that ingested mealworm will eat their way out of a reptiles stomach. a little common sense will readily dispel these myths. consider that the exoskeleton of all insects is made of the same chitin found in mealworms, and that thousands of lizard speciese in the world owe their very existance to the daily consumption of these chitinous insects. in fact, many insect eating lizards produce a enzyme called chitinase that breaks down chitin.

mealworms are safe.

I can assure you, mealworms can cause issues. I have been dealing with leopard geckos and other reptiles for fifteen years.

They are not just myths and just because an expert says something does not mean you should follow the information blindly.

Mealworms have very strong jaws. The superworm variety mostly, you don't really have to worry about it with the mini's. I personally crush the heads of superworms, but that's if I ever buy them. I generally don't waste money on them since they are so low in nutrition. I mean, put some lunch meat against a superworms jaws and you can see how easily they would be able to eat through the internal lining of a reptile's belly.

A diet of mealworms should be avoided since they contain very little nutrition and a lot of chitin that can build up in the digestive tract over time [or very quickly if you're feeding too large a worm to a leo]. Waxworms, butterworms and mealies should be given as occasional treats and not as a staple food every day. There is a reason waxworms/butterworms are called "Leo Candy" because they are high in fat and should be a rare treat or used with leos that need to gain weight back.

Roaches are the best staple. They don't have hard chitin [adults can have it, but adult leos are too small for a full fledged adult dubia], come in a variety of sizes, are nutritious, and can be bred very easily. Crickets come next, then phoenix worms. Mealies are honestly a shit feeder :/
A lot of people feed them because they are cheap. But get a roach colony going, and it costs less than $10 a month for upkeep of a colony. Easy, nutritious feeders, available in all sizes. And if left to breed for a little while, you can have a colony of 10,000 within your first 6 months or more. All the roaches except for adults are rather soft and squishy too. They also won't chew on your leo's, which makes leaving them in the cage easier.

most every reputable breeder ive ever associated with has used mealworms as a primary staple. and when mixing a variety of other foods its surely even better.
and of course you want to make sure the corrrectly sized worm is going to your gecko, you wouldnt give a adult worm to a baby gecko. and i hardly think its fair to compare a sliver of ham to the intestines of a reptile that spends its lifetime eating living bugs. no, i wouldnt give them superworms, but mealworms are smaller, smaller jawed, and would swiftly die from being chewed and suffocated

and for what they may not get nutritionaly from the worm, you are dusting them with vitamins and suppliments. and if your giving them a plethora of different feed its not a issue

tho, variety doesnt hurt ;3 like butterworms, hornworms, waxworms

Ahhh, what a little cutie