After watching the movie several times ,here is what i think about Gogeta's power level.
Broly is unique saiyan whose power level rises each time during fighting.
Ikari form of Broly powered upto the state where he equalled
Full Powered Perfected SSB (FPPSSB) Goku. Broly was only struggling because he isn't even close to the level of Martial skill Goku used.
When Broly transformed into SSJ he get's minimum 50 times multiplier over his Ikari base form he was using before. SSJ Broly when first appeared he effortlessly beating tag team of Goku and Vegeta both in FPPSSB so much that they were basically flying away from him. Then he clobbered Frieza and Golden Frieza for 1 hour. After that SSJ Broly again powered up before he went to fight Whis. This Powered up form may be 2 to 10 times stronger than before. That makes him closely more than 100 times stronger than FPPSSB Goku.
Now when Base Gogeta appeared he effortlessly dodged all attacks of powered up SSJ Broly, broly wasn't able to catch Gogeta by speed. That makes them more or less equal in strength.
Base Gogeta= Powered up SSJ Broly= 100 times FPPSSB Goku= MUI Goku= ( FPPSSB Goku+ FPPSSB Vegeta) times 50.
Gogeta goes SSJ to completely dominate the powering up ability of SSJ Broly.
SSJ Gogeta= 50 times Base Gogeta
SSJ Gogeta completely dominated SSJ Broly until Broly transforming into his LSSJ form. Gogeta transforms into SSB to regain the upper hand.
Now we don't know the perfect multiplier for SSG and SSB transformations ,but roughly
SSG= 100 times SSJ3 and SSB = 50 times SSG.
SSB Gogeta = 50 * SSG Gogeta= 50* ( 100* SSJ3 Gogeta)= 50*{100*( 8* SSJ Gogeta)}=~ 50000 SSJ Gogeta
That's too large power level. FPLSSJ Broly blocked two kicks of SSB Gogeta forcing him to go full power and continuously beating Broly up without allowing him any time to power up even further.
If Gogeta used evolved version of PSSB then multiply it again by 20.
NB: Ikari Broly multiplier may be 100 times of base, considering Base Broly may not be stronger than SSJ3 Goku. Even in Ikari Form Broly continuously powered up. As Ikari equalled Vegeta SSG form,