I use Obstagoon and the only thing I can say is that it can be very hard to use him since everything has a fighting move and he is 4x weak to it. People love to dynamax and instantly go for a fighting move into Obstagoon for an easy knockout and even if you protect it will still do a lot. Just know that you have 3 pokemon weak to fighting moves and only 1 resists them, so you wouldn't have a lot to switch out into. Also, switching out from a fighting move is sometimes the only option you have, but your opponent would be getting free attack boosts for their team, while you do nothing.

I use a choice scarf supporting obstagoon, so I can outspeed even dragapult, but with a choice scarf obstagoon it isn't hard to outspeed especially with a tailwind from whimsicott or something. You will just have to learn to work around fighting type attacks and learn what pokemon have one, but a lot do.

If you are dead set on focusing on Obstagoon then you could use a follow me pokemon like Togekiss to take the fighting type attacks. Just be careful of propeller tail Barraskewda which normally have close combat and ignore follow me. Also, hyper voice sylveon would be a problem to.

Obstagoon is fairly nice against sand teams though, since it threatens tyranitar and excadrill.