I guessing this person has no idea about armies or soldiers, and has no creative drive to imagine how an army in a magical fantasy world would probably Tdeviate hard from a lot of real world norms. Not to mention the tradition of fantasy mercenary forces with OP abilities. #TTRPG https://twitter.com/mattcolville/status/1297242386066599936

This reads like it's coming straight from the "soldiers are background fodder that make the adventurers look good" school of dull world building where people are somehow oblivious to the realities of the world around them and the adventurers (Player party) are somehow tuned in.

I participated in a panel about this a few years back. The TL;DR is that, in a consistent world build with regards to monsters, magic, and so on, military conflict would be very different in comparison to warfare in antiquity to the middle ages.

Q: Would fantasy militaries know about the abilities of adventurers?
A: Yes, because they'd have be able to fight it on the battlefield and provide security against it in camp and fortifications.

Q: Would fantasy soldiers know about monsters?
A: Yes, because they're the ones...

...holding them at bay and doing the routine fighting when adventurers aren't available or cost effective.

Q: Could fantasy militaries clear dungeons?
A: Yes. And they'd probably be more brutal and savage than any adventuring party. Only things like mega dungeons or ones with...

...exceedingly powerful inhabitants would likely be considered "unclearable" because of the materiel and personnel losses. Places like that would likely be picketed and monitored, with "specialists" (read: adventurers) being allowed to conduct raids/incursions.

Q: Wouldn't militaries just be boring NPC classes?
A: No. Trainable classes like Artificers, Alchemists, Fighters, Wizards, Rangers etc... have direct military applications and would likely constitute large parts of elite units, leadership roles and so on. They're an investment.

Q: Why would adventurers find work then?
A: Because militaries can't be everywhere, all the time, and in full force. Then there's "off the books" work, work for civilians (nobles, villages, academics etc...), and specialist services that are too niche for militaries. Plus...

... there's always new dungeons or ruins being discovered, and random encounters where the adventurers can be right place, right time. And that doesn't even get into the quest model of adventure design, so there's lots to do and be famous and loved for still.

Q: Why would fantasy worlds have so many standing militaries?
A: Because security is a nightmare. Monsters, magic users, bandits, the list goes on and on. In a conventional fantasy world (sword & sorcery, heroic fantasy, or high fantasy), having a standing military isn't an...

... option. It's required. Even a lone homestead would look more like a fortified compound than a real world house and barn out on the plain, and would likely have at minimum a sentry posted at all times, if not a roving patrol, just because the threats are complex and constant.