There is a fine difference between
Broli's potential limits
and
The power that Broli showed
Broli is strong, no doubt, but at most he'l be Ssj2 if he REALLY went all out seeing as though Ssj2 was considered the real NEXT step above Ssj1 in a similar way that Lssj was.
He has the POTENTIAL to reach Super Saiyan limits in power through his Lssj form, mainly the power of Ssj3. BUT Broli NEVER achieved this because he was disposed of, despite coming back 2 times he still never managed to fully maximized his limits.
Broli is DURABLE, not invincible or god like. Completely different.... considering the Saiyans and Piccolo were not as strong as they could be when they fought him.
Oh and wait... they practiced, got much much stronger, concieved Trunks and Goten.
Who....
yup...
held their own quite well against Broly.
Sooo.....