Attacks/Supports are most efficient when you have matched WLs with anti-troops. Timing attacks also gives benefits.
These benefits are easily spoiled by someone joining "not invited by mission leader":
- as joining with a strong WL changes the matching of all weaker WLs,
- joining timed mission from distant tower/ark makes the target visible significantly earlier than it otherwise would be the case, thereby removing the element of surprise.
- this would also make it easier to play on mobile as it is OK to join any missions you are able to without spoiling troop matching.
proposal: enable the mission leader to "lock" participation (disable JOIN) on a mission when optimal composition is reached. Also enabling "unlock" if there is later need to add WLs.