That's not logical deduction at all, sorry Escape , so let me explain to you how.
Ah, I am glad to know that only you can deem what is logical deduction. I see that you've come down with the same disease that plagues many debators these days: logic-god syndrome. The condition in which one thinks that one's opinion or one's verdict supercedes another's. Especially when that person (unlike GM Nebaris) has not been shown to defy canon or defy authority.
#1. Brand has no idea how many Jedi it will take
Considering how Brand is a surviver of Order 66 and that DE Sidious was the one who mortally wounded him, he would be in a position to accurately judge how powerful Palpatine is. Say, unlike Luke, when he made the "judgment" regarding Marka Ragnos. 😉
#2. Since he knows and we all know DE Sidious is uber powerful, why not use them all, better to be safe than sorry.
Mm-hmm. Brand says: "The Force and the Jedi before us will see to that."
I believe that The Force - being omnipresent and omnipotent - would have a fair assessment of one of it's prime users (Palpatine). So quit trying to undermine Palpatine here. And, furthermore, say you're right. Let's say that they all did it "just in case". Consider then that they wouldn't want to take the chance.
It's the same with how I argued for Exar Kun, and I understood the fact that they rallied all the Jedi against him, but it didn't necessarily take ALL the jedi to defeat him. Understanding yet?
It's moreso illogical to assume that it would take only a handful.