This has been said multiple times: Thanos, even without the Infinity Gauntlet is one of the most powerful people in the MCU. So even if he didn't have the Gauntlet with 2 infinity stones already, he could've probably wiped Thor out like a fly. Also, I'm not really sure what you're asking during the second question, what scene exactly do you mean? Are you on about the scene where Strange, Tony and Peter are on the Q ship? If yes, then it's like Tony said, you saw what they (The Black Order) did on Earth he wanted to get the fighting away from Earth and fight on "their turf", as Thanos wouldn't expect them to show up to fight him on Titan.

1) Thanos is the most powerful being in the universe.

2) Strange isn't powerful enough for his portals to send people halfway across the universe.

Yeah I meant before Tony suggested to take the fight to Thanos, but that makes more sense.

Dr Strange's sling ring can only send people in the closest distance to him to a far away place, not vice versa.

If Dr strange had done that, would there have been the cool Titan battle... No

I'm assuming he lost in a similar matter that Hulk did. I'm curious to know if he put up more of a fight though.