kooturtle
I think you're setting players up for failure in newbie spaces if you aren't strictly enforcing meta play. In my mind you have to crawl before you can run. The goal of these spaces is to set new players up for success in the 6s community and one way that's done is by restricting the amount of situations that they're going to see early. Being brand new to 6s is very daunting and there is a ton to learn before you can start getting dubs (the fun part). Most new players I have worked with have trouble with the idea of a soldier bomb, or a flank, or holding a door, or even using voice comms. They need a place to get reps in so that they can start to understand the nuances of these simple interactions that better players take for granted. Throwing pyros in the mix is just too much.
Once they have an understanding of the basic concepts in meta 6s, they can start being exposed to the more niche ones. Offclass play is weird, and trying to get the average newbie pug player to adapt to a heavy or whatever in a push is just going to be frustrating.
That said, its obviously not immediately frustrating for that heavy player. They get the cool dopamine hit off the kills/ W/ successful push/ whatever. They however are not learning the absolute basics and will be completely lost when thrown into a more standard game of 6s. These are the players that join tf2center and are immediately mad when the other team just rotates away from them on heavy. It will hinder their ability to find a team, it will stunt their improvement, and make them worse in the long term. It is unfun to be bad.
Off-meta play is super cool and something that I like seeing in league play, but its only ever really fun when both teams understand the implications of what is happening and have the tools that they need to make adjustments. Most new players do not yet have the tools to make on the fly adjustments at that level and will just get stomped by a heavy/ pyro/ sniper for 30 minutes and learn nothing. They leave frustrated and nobody wins.