So I played that mode all day long and found a pretty easy & good strategy to get some easy wins. The last hours today only were played by doing this and got me a pretty good winrate:
Prepare some fast heavy tanks/brawler like Obj. 277 At start of the game. Choose your best tank for that map that you prepared in step 1(depends if its flat/open/hill/city map) Ping the flag right at the start if the game, so other people know what you guys want to do. Ping again if you can. Now the countdown is over and you rush to the flag point. (Ping it again in case some teammates forgot that you want to cap) When you at the cap try to go Hulldown or in cover. (Dont go afk, you should peek for shots/spot and help your team) Now there is pressure at the enemy team. Often the enemy team got only half their team on the cap-side of the map. Here you need to decide if you want to keep cap or rush the enemy half of team on that side with your full team. (Show your team what is better by ping) If you cap dont worry if you get reset by arty strike. Just keep cap.
If your team works with you nomally the early cap pressure/ one side rush will win you the game. Other times team wont listen and then you may loose. But I would say at the lower ranks 60% W/L should be able to do with this 🙂