Remathilis
Legend
I think part of the disconnect is that it's very easy to conflate the Known World (the vaguely defined setting of early basic modules and box sets) with Mystara (the setting developed around it through the Gazetteers and later box sets). The setting as told though the Basic and Expert and early BX modules is fairly low magic. It's also barely Mystara. The Keep on the Borderlands is not a fair representation of what the setting looked like come the Princess Ark.The core of the setting, as expressed in the core books, is what I'm talking about. Thank you for at least acknowledging that as opposed to trying to gaslight me.
You can map that same trajectory to Greyhawk (Gygax's folio is a very different setting from the Living Greyhawk Gazetteer) or even Forgotten Realms itself (the original books are lower magic than the setting would eventually become). You can't judge a setting purely based on its original version.
Which is why people took such issue with that characterization; it doesn't reflect what the setting became, only what the proto-setting from which it emerged was.