Keep in mind that Broly destroid a whole Galaxy while Kid Buu only destroid a couple of planets.
Mystery about Brolly power level and his strength compared to other Z fighters.This has always been a mystery. We do not have any official source for Brolly's power level and all we have is different board users giving their facts and stuff from manga and movies etc. Most of the time I have found that many of the manga followers discard movie based facts to be non-cannon while arguing. But then Brolly himself is a movie character so facts from his movies must be allowed.

Most of the time he has been declared to be weaker than USSJ and SPC. But probably we do not have enough evidence to prove this. Lets check the facts we know from the movies/manga and try to come up with where Brolly is in terms of power level:

1. Brolly could destroy galaxies as King Kai mentioned in Brolly's first movie. At that time we knew that some of the Z heores and villains could destroy planets but I don't think anyone known to destroy galaxies existed.

2. In Brolly's first movie Gohan was a SSJ and Trunks was also present so it can be assumed that this timeline was post ROSAT and Pre Cell games. So which means Brolly almost destroyed 2 FPSSJ (Goku & Gohan), 2 USSJ (Vegeta & Trunks) and 1 Super Namek (Kamicollo) with ease. He however underestimated Goku and let his guard down and started toying with him and got hit badly. He however did not die as we know that he was kind of put to hibernation.

3. In Brolly's second movie he fought adult Gohan (who was > 100% SSJ and < 100% SSJ2) and 2 SSJ and wa able to dominate them with ease and then as usual went on his toying mode and again got beat by a combined effort of the live warrior and a spirit Goku.

4. We know that Brolly can survive in space and under lava as shown in movie which I am not sure if any other Z hero or villain can do (survival in space excluded).

Based on the facts given above it can be concluded that Brolly > SSJ, USSJ, FPSSJ and Adult Gohan on a one on one fight

Now for SPC. We know that SPC matched a badly injured SSJ2 Gohan in Wow power leveling who was fighting him with only one arm. I have heard many users say that when a Z fighter is not powered up then he is vulnerable to attacks. But we very well know that SPC was greatly powered up and was in a Kamahameha beam struggle with one armed Gohan but was still distracted by an attack by an injured Vegeta who was < SSJ2. So this means that either he was not all that powerful because he a) got distracted by a weaker fighter's attack and b) he lost to a badly injured one arm broken SSJ2. By this I conclude SPC < Badly Injured SJJ2 Gohan (who is surely not at 100%)

Based on this I assume that an Adult Gohan should be close to power to a badly injured one arm broken SSJ2 Teen Gohan. By this I conclude SPC < Adult Gohan.

Hence Brolly > SPC on a one on one fight.

Now some times I have also found USA13 (Ultra Super Android 13, his final form) being compared to Brolly. We know that he fought either 3 SSJ (Goku, Vegeta, Trunks) and 1 Namek or 1 SSJ (Goku), 2 USSJ (Vegeta & Trunks), 1 Sayian (Gohan) and 1 Super Namek (Kamicollo). Initially he owned them all but later fell for the spirit attack after distraction from Picollo. So in any case he did not take on the same combined strength as Brolly did and Brolly sure took care of 2 FPSSjs so we can conclude Brolly > USA13.

Now Bojack. He took the same gang that Brolly did in first movie but minus Goku. He owned them all and then got owned by 100% SSJ2 Gohan pretty much just like PC. So Bojack should be in the range of PC's power level or max SPC's power level and hence Brolly > Bojack.

Keeping all the above facts I have given above we can form a strength comparison chart pretty much like this which should be correct. All below given forms are at 100% power:

SSJ2 >= Brolly > SPC, Bojack, PC, USA13, FPSSJ, USSJ, SSJ

in a one on one fight.

If anyone has any disagreements about this or find that I have made some mistake in the facts given then pls post your opinion and facts supporting that. But pls don't start by saying that movies are not cannon. We are discussing a non cannon character so non cannon facts must be used.