Hi!
Thanks for replies!
TBH I misread the sword brethren somehow. I thought they had the same shooting attack as Tac marines. Well that makes a difference.

Testing will tell how much.
Emperor's Champion: Fluffwise he is correct as you have written. Fearless Marine CC hero, seeking enemy chiefs / champions.
But idk, maybe UK version planted the bug in my ears. They have him as an additional character, with inspiring, leader, invu, fearless and MW extra...now that's really heroic!

I mean it may affect nearby Marines seeing him (inspiring?), as their Chapter's chosen one, fitted with the best weapon and armor available to them.
Also it is part of the story if the champion falls, it is a bad omen for the Black Templars.
So I think if you want to go with the fluff, and have players take this iconic character [not by enforcing it], it would be useful to make him equally good or better than "ordinary" Marine characters. For drawback, he should get the same rule, which many other list has for it's super-unique stuff.
If the Emperor's Champion dies, all Black Templar formation within LoS receive a Blast marker.EDIT: These are merely suggestions / opinions.

I will try it out anyway, whenever I can persuade my SM opponent to switch armies. (I only have a large IG army, currently)