Ignite the spark era battle requirements

Not to complain, but when I have an R7 team with some speeds over 300 vs an R5 team (-3 relic delta), why is it that the event isn’t passable. I’ve done multiple rounds, tweaked, nothing.  If by R4 you really mean you need R10 or forget it, just say so. Because once I waste resources and a lot of time to still lose repeatedly, what I really don’t want to do is invest any more in era toons.  You understand this is a game right?  And people play to win?  There’s a challenge, and then there’s just frustrating gameplay.