Conqueror works well in lane but not in team fights....

Which is fine tbh. It's a really good splitpush setup, just like a rageblade in a build would. It might be overbearing if it was as good in teamfights.

Working as intended I think

I feel like its good in teamfights for specific champions like . Some prolonged fights she can clock in like 1000 true damage.

If you build Glass Cannon then ya i imagine it doesn't work as well. If you build some tank i'm sure it works fine.

Yep. And 3 weeks into pro play no one will take conqueror.

It's not intended to be as good in teamfights as, say, Press the Attack. Otherwise there'd be zero reason for any melee to take Press the Attack over Conquerer.