Argyle King
Legend
Couple of things.
1. Train Your Dragon 3 is PG-13. It has, apparently, drugs, sexual content and naughty language. IOW, it's more adult content than Dragonlance.
2. Dragonlance at the time was marketed to the YA fantasy crowd. DL was never intended as an adult series. The primary audience for DL was the same as Harry Potter, or, now, How to Train Your Dragon. I'm frankly rather baffled how you came to the idea that DL was meant for an older audience.
So, with that in mind, why do you think that DL is a mature audience series?
I haven't followed the whole exchange, but the last part of what you said here caught my attention.
I would dare say that Young Adult books from that time period were open to exploring themes which might be viewed as inappropriate for contemporary YA.
I'd be surprised to see Black Cauldron made into a Disney film today -despite it being toned down from the books.