Why does Jack seem strong he didn't really destroy anything of great size(despite his). He has great endurance that's for sure and he survived an unknown battle with an admiral but Law survived an assault from the same admiral and Doffy just to put some perspective on it. Also the Marines don't just go out and antagonize Yonkou territory, they left WB territories to him also, The samurai are probably very strong a well but a main reason the WG let them be was because a Yonkou was in control of that land, it's not that they fear the Yonkou they fear what happens when one dies, like they were afraid of the power struggle that would come about at WB's death, they were more worried about that potential outcome then the battle.
They were completely scared at the thought of two yonko meeting up, they do fear kaido, he is amassing an army and took over a very powerful country. They fear a yonko dying as well because of their strength and reputation and things would go to chaos without them.
Jack fought for days and then immediately went into a high scale fight and came out decently well, he has a 1 billion berry hype. He has all this hype for a reason. Endurance is extremely important your point is? Jack seems to be quite fearsome, its not far fetched to say he can give issho a good fight, similar to how marco is considered quite strong.
law was kept alive due to the fact that issho wanted to handle things that way, is that the same for jack absolutely not, so you'e comparing apples to oranges. plz don't use weak logic. a lot of this base has a bad interpretation of hype, jack was portrayed really well.