Can you explain what your concern/problem/question is?

Meanwhile, gear upgrade missions were implemented to upgrade the gear for events' crusaders after the event took place. So far, this is the only possibility to upgrade gear for these kinds of crusaders after an event has finished. If I understand you correctly, this mission is a chance for your crusader without any gear to get a common gear for him/her/it.

In order to succeed these epic missions, you ideally need an EP level of 200, at least epic gear on each crusader and all the required tags.

A few remarks: That you can't reach 100% chance to succeed the mission is an intention. This way, these epic missions provide a chance to upgrade the gear, not a guarantee.
Therefore, it is also intentional that some of these gear-up-missions require the tag only the event crusader has, even though this specific event crusader doesn't have 200 EPs nor the best gear and might not be the best choice to add to the missions' group.
Therefore, it is also intentional that you might fail a lot of these missions - I did in the past, too.

ah, I think I understand, thanks for the explanation :-)

Well, yes, it is quite difficult and immensively time consuming to first get a past event crusader and upgrade its gear to all rare. Especially as there is a 1 in 3 chance everytime which gear is upgraded - meaning, after nine of the gear missions, you could end up with two epics and one common gear as far as I understand the logic.

But even though it seems like a chase of the horizon (new events and therefore new crusaders coming in faster than you can possibly upgrade the 'older event crusaders' gears'), I personally think it is a nice bonus. If these missions weren't there, there wouldn't be any chance to get older crusaders, nor to upgrade their gear ever.

Would I love to have event crusaders' gears included in the jewel and silver chests drops? Of course, I would. Would I love to see more epic gear missions (reducing their cooldown, having more than one in parallel)? Sure. But I also think this might make this whole thing too easy and would change the focus of the whole game. And as far as Erika has said in the past, missions are not intended to play a center role in the game, but to be something like a gimmick.