@Orange if SSJ2 is only a 2X amp of SSJ1 then Goku would not need Gohan to beat Cell if he can reach that level by stacking his mastered SSJ state on top of Kaioken X2, both of which he’s trained to the point he won’t lose any stamina or break his body in the process as shown and stated in the series. Cell would not be scared of SSJ2 whatsoever since he has Saiyan saga Goku’s DNA, who knows the Kaioken up to times 2 without breaking his body.
If SSJ3 is only a 4X amp of SSJ2, meaning it’s an 8X amp of SSJ1, then he’d just need to stack kaioken X8 with normal super Saiyan to achieve the same level of power without worrying about stamina or energy issues.
The only multiplier in any of the SSJ forms that makes any form of sense is SSJ1 since it’s far beyond Kaioken X20, something Goku tried to do on Frieza and it failed on. The others do not make any sense no matter how you look at it as it contradicts the story if we’re to accept the Daizenshuu’s multipliers.