Do not worry, you still can chose to play lowlevel node on Venus. And there are some super cheese builds to deal with Lich/Sister, like basically any Warframe with invisibility, Loki/Octavia is an absolute cheese to kill them. And sisters are much easier grindwise then Lich. I did 2 Sisters in one Sunday, and my account like 1 month old.
Do not worry, you still can chose to play lowlevel node on Venus. And there are some super cheese builds to deal with Lich/Sister, like basically any Warframe with invisibility, Loki/Octavia is an absolute cheese to kill them. And sisters are much easier grindwise then Lich. I did 2 Sisters in one Sunday, and my account like 1 month old.