I know of at least one mission that requires you to join a clan, another one that requires you to get three activity stars and a few that require you to get a certain amount of damage on specific clan boss difficulties. Those ones can be found in the Arbiter mission chain and unfortunately there will be no way around those.

What mission are you referring to, specifically?

By refusing to join a clan you are hurting yourself. You cant progress in missions, You will NEVER get any cruel or imortal gear or any of the cvc rewards. 

Why not? you might even make a friend?

Leveling up a referral account makes me realize how unprepared the game makes players in joining a clan and using cb keys.

It is probably the most important part of the game but it seems 98%(random anecdotal number)of new player accounts ignore this.

Early missions really should get reworked in order to better explain and guide new accounts.

You could join and leave any clan just to complete it ...you can also just join a random clan and never look at the clan chat tab ... lots of clans have no requirement , no rules .. you wont even notice their existence :P

You'll get access to a clan shop (has energy , books , fragments , etc) and clan quest which gives you the currency to buy in said shop. You'll also gain access to CvC and its rewards(every CvC has rewards even if its a loss)

And the most important part is Clan bosses .. but you can go around that simply by making your own 1 man clan iirc ! Being in a clan with 29 other people also enables killing CB for 2x chest reward ..

Tons of ways to go about it... just dont forget your options ... they will be there later too so any choice you do make isnt permanent ...

My reference is with the Progress Missions, I like this game for relaxation, I am actively involved in another interactive game alliance so I really don't want another alliance, I lose a lot of battles, but I enjoy seeing what various champtions do against other more powerful champions....

Yoda, I been stuck on progressive mission for now almost 2 years.  Wait till you have to fuse RHAZIN.  

If you care more about completing the progress missions than you do about getting demon lord rewards, we'll, there's really just no point to playing the game.  Demon lord rewards are really worth more than pretty much any other content rewards.

There is a very simple solution to this problem:

Make your own clan, restrict membership ans be the only one in the Clan...than you can also do the Clan Boss and do not need to bother with other players

Not need to create just join to free one and leave.

Yep, but that way you cannot do Clan Boss

Yes, he cant do, but he just want to complete clan mission.

But the thing is he will have further clanboss missions like do 100M points on given difficulty.  He would have to join again, and would never have had the opportunity to build a team capable of even 1M.