Op and Yolo Han Solo is referring to a Summoners War (probably other games has this too) feature that a player can have a representative champion which a friend in your friend list can borrow this champion to any content you like (except pvp content) for only one battle a day.
But since Raid has no friend mechanic in this game, the op is trying to use clan instead. Thus, giving clan more purpose other than just clan boss.
I believe he is saying clan have no purpose is a sarcasm. Honestly even I don't join a clan I can still play the game normally.
So what is the advantage of having to use a representative champion of your clan mates? In Summoners War, if your friend's champion is a campaign farmer, you can use them and it will not eat up exp, thus giving more exp to your champions. Imagine this having to run 50 times with extra exp for your champions as a f2p.
Another is, like what he mentioned previously, you can somewhat 'try' your clan mate's champion if you don't have this champion on yourself.
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I just want to add, this is a bit off topic, Summoners War and other similar games have so much QOL updates and features on their game that Raid is missing. Raid has poor QOL features that this game feels like the first two years of Summoners War. These features are already available in other games while Raid is just focus on creating champions and harder contents, while doing this, they should nerf older contents for new players to catch up om the contents easily. But no, they don't even think of this. So contents are frustrating and overwhelming for new players, if there is really any serious new players.
So when new content comes out and new-ish players can't enjoy, what do we say..? This is end game content. This is what we say when faction war was released. This is what we say when 3v3 was introduced. And when doom tower was released. Now, this is also what we say when Hydra was release. Almost everything we see now is "end game content".
They should make Dragon, Ice Golem, Fire Knight and Spider dungeon easier so newer players can quickly enjoy end gsme content, but no, they actually make farming in dungeons harder by indirectly nerfing Seer in stages 21-25 of dungeons. And what we said to players struggle on this stages.. This is end gsme content.
This is the future of Raid, the direction they are going with.