Broly's was never once stated to have unlimited Ki, only that his Ki was rising, to assume so would be NLF
Yes Frieza would be one shot by Broly but you stated that SSj Goten and Trunks were greater than SSj2 Gohan, however they've been stated to only be around Frieza's level
SP Cell wouldn't die in just a few hits, Broly would have to erase every cell with Ki, he cannot do that with physical attacks
Broly doesn't have many strength feats, him casually raping the MSSj Z warriors is a feat that any SSj2+ being can do, Hell as shown by Akira (the Z universe map) is around the same size as the universe itself, Broly isn't destroying it (putting hell down was my mistake I forgot the OP had a different setting)
Kid buu doesn't need LARGE blasts to destroy planets, when he first appeared he was going to destroy Earth with what looked to be a generic Ki blast, however it was repelled by Vegeta it was then that Buu decided to use a large one. Buu isn't weak, he has the best canon feats in the series.