Don't join a guild in game.
There is no way for the guild to set it so only people with 7 star characters can join. The vast majority of guilds have raids on farm. A player playing less than 3 months can solo heroic pit. Heroic rewards are much better than non heroic rewards so most guilds will only let people in who can take part in heroic raids.
Discord servers or the recruitment section here is best. If you dont want heroic raids find somewhere running raids that will suit you.
You can always take part in heroic raids with a single character. It mightnt help the guild much hut at least you get rewards.
