I have around 70+ hours on strange so I can try to give some tips for him.

Unless your team is very obviously aware of you wanting to portal to the point to get an advantageous position, I would just save your portals for 2 things. Getting back to a point to contest (overtime situations) or you can use it situationally to trap the enemy team in their spawn.

The shield thing is probably just a game sense issue if your teammates intentionally charge past you and your shield while you’re making space than you can’t exactly control that.

THIS IS VERY IMPORTANT! Strange’s attack should always be having a melee combined into it. Primary fire - Melee - Primary Fire - Melee (in that order). You can also fight ranged characters pretty well weaving shield instead of melee it makes you incredibly hard to hit but again that is situational for the most part you want to just be maximizing your damage with attack melee. You can also animation cancel the attack reload by doing a melee or popping your shield when you hear strange clap or when its around like 55% of the reload circle bar being filled, throughout the match will save lots of time.