Play with B and C team

Too many heroes and many of them are still not eligible for use in my main team. Just unlocked Heckler: completely useless in PVP if I put him in my main team with 9* - 7* heroes.
What’s the best method for using a B team? A team with lower level characters that is. I feel that using strictly 5* heroes will still match me against 8* - 9* enemies.
Should I stop leveling my B team up at 55 or something?

My B team is level 70 and works quite well. Sure not as good as my A team, but its good for good share of wins. Why you are matched with 8* or 9* heroes i don´t know.