Here is the Japanese literal translation :
Elder Kai : 超サイヤ人になるなら合体したあとでなったほうがええまそんなことせんでもじゅ~~~~~~~ぶんじゃろ」ポタラのパワーは それほどすごい!
Elder Kaioshin: "If you’re going to become a Super Saiyan, it’s better to do it after merging. But even without doing that, it will be mooo~~ore than enough. The Potara’s power is that incredible!"
So in the original, Elder Kai showed more confidence still than in Herms'. じゃろ (jarou) translates to “will be” or “should be”, still though it carries a tone of confident assumption rather than 100% sure. It’s more like saying “I’m pretty sure” or “it should definitely be” rather than outright declaring “it is guaranteed.”
But still, the Japanese version feels more confident than the Herms' wording, implying that base Gokhan would likely be very strong, with transformations as a backup if needed, but leaning closer to a large gap, but still not a guaranteed blowout.
The "probably" used by Herms more than likely slightly weaken the tone compared to the original Japanese, where Elder Kaioshin comes off as being more sure that the fusion’s base form would suffice—though still allowing for minor caution just in case.
How you you interpret it though?