in 2 years Goku went from a power level of 1000, to stronger than Final Form Frieza. Because Zenkai Boost is not a good reason. The Zenkai boost logic is fine, but each one is inconsistent in how strong it makes Goku/ Vegeta/ Gohan. Goku went from 180,000 fighting Ginyu to stronger than however strong Final Form Frieza is, significantly stronger than 2 million.
How?
2 years?
He went from a PL of like 400 to stronger than Final Form Frieza in just over a year.
The Saiyans arrived about a month earlier than expected (11 months post-raditz). It took bulma krillin and gohan about a month to get to namek, then goku a week to catch up with them.