Every one do not want me to add a comment here so i'll start :
running offclasses in different situations can always be viable for a team, as long as they know what they're doing, if they made a plan before. you don't make your team better by taking offclasses at random times for fun/ to make the ennemy tilt. For me, se7en has the best use of non-standart offclasses, because usually starkie has made a strat around it.
But thing is, se7en is worldwide known as one of the best team of the world + a very fair-play team to play against, so you know they won't try to troll you in scrims, result is, if they offclass, you know that's a strat.
Let's now imagine, a team running full pyro most of the games BECAUSE they think it is viable for them. I can tell by experience that at first, every one will try to make think it's stupid, that it doesn't work even though they've never actually try to do strats. We, in DABZLANDS, had the chance to be really united so they trusted me, but i think for most teams, if you get shit on everytime you play because a guy in your team tries to make his stuff happen, it's more likely you'll not trust a lot your team guy. Once you made it clear that you'll play with this offclass strat in officials matches, and gain some street cred in terms of performance. you'll encounter different type of teams to scrim against :
-There will be the teams that just think you're a clown, and so they will not scrim you (+ in some cases insult in public forums and so on...)
-Teams which will not scrim you BECAUSE it's too unique. It's a fair point that i agree with, because if you're not in direct opposition with this unique team during your season, it is not useful to scrim them, as they're playing differently.
-Finally Teams, very rare ones, that wants to scrim you because you're playing unique, which is for me a good thing to do (Special thanks to the polish team of s28-29, who even adopted this strat back then, and also the russian team with dima, and obviously ringo squad)
Basically, you don't get a lot scrims, so i remember i had to swear to the ennemy team that i won't go pyro during our scrims. which is disapointing.
As it stands today, if you want to make your off-classing strat a real thing, you have to look clean and friendly, having a team full of good dudes, being at least known for being good at the game, not listening to the community of people harrassing you to stop it, and practise against the very 2-3 same teams which has agreed to play against you. That, along with many other reasons, is why we don't have a lot of these nowadays.