Look, I have no problem with the whole Gundam battle tournament thing. I have no problem with the power of friendship. I have no problem with having Gundams from all of the series in one show.
My problem with Build Fighters is simple: THOSE ARE NOT MECHAS, THEY ARE TOYS! PLASTIC TOYS!
If they kept the show exactly the same, but used actual real, huge robots (kind of like G Gundam), I would have no problem. And don't say that it would be unrealistic to have kids building actual mechas. They have magic particles that move plastic, realism flew out the window.