Ummm... No. I only get to use a player avatar if I receive it as a prize. This guild avatar you are proposing will be available to all guilds whether won as a prize or not.
So what ?
All you have to do to get a "Portrait" is get to the end of yet another "Event", that is not hard to do because all you have to do is play the game daily.
I don't even want Avatars in these Events period, it is a junk prize. I have used the same Avatar for years. I also remember a time when Avatars were just handed out to everybody before they were part of the Event payouts. I don't get what you have against evolution.
I want better rewards for my time and effort in Daily Challenges / Events / GE / GvG / Quests.
Put all Avatars in the Daily Challenge payouts rather than the useless junk it often hands out or, use the old system of just putting them automatically in the Avatar Cache.