Proper managment of food champs alter arena algorithm, but it not solve anything if you not have good arena team or have flaws in champs lvl /gear.
Best example is as player level around 48-50 wiht PP 700k cannot go above B1/B2, putting aside arena team his PP is over inflated so even in B1 alghoritm will choose opponent from 48-50 with powerful champs
(Im 53lvl with PP 401k, on the edge for arena alghorim, as when i drop to 380k getting better match/win ratio for my team)
Other flip of the coin is knowledge/experiene of the game (if you do silly things you get silly results)
That's why HH, Ash or GumpyJeff vids and web pages to fill the gaps.
Other thing for F2P is high resource management and patience, you keep champs which you need (based on HH ratings for example) and food anything else to get your main champs better.
As you said 50lvl Kael, Elhain, Shaman, Warpriest it is entry point and you will be in arena B1,
upgrade Kael to 60lvl and you will propably reach B1/B2
amend gear (farm higest possible dragon for gear you need), ascend champs put some masteries and over time you will sit in B2 etc ( it is evolutionary progression over time)
I use daily 30 auto runs for farming ( usally 15 dragon, 15 spider ), time and patience is a key for F2P Raid player