But I don't get your point, why is it fine for Mecha to be very similar except for some few things but not Sports, when it's the same way?
I think Ping Pong is a pretty unique show, but I don't watch that many sports shows. If Teppuu were to get an adaptation, I would gladly watch that.
You're right that most Sports shows are heroes team vs rivals team, but the differences in the shows are why people watch them in the first place for nearly every genre.
Because even cookie cutter mecha anime has a little bit of imagination. How many times you want to watch people kicking balls around and screaming even if it's "unique"? you can get that character drama everywhere without wasting your time and actually watch some cool action instead!
Sport anime are fun for the interactions and relationships between the characters.
Sure, you can have that in every other genre too and generally you have that! without all the boring sports fillers.
If I want to watch sports I go watch sports, not anime