Korra has a very large recurring cast of members. If you watch the show and compare it to ATLA, you'd notice how big the TLOK cast is, but more importantly, how much screen presence and development they have in comparison to ATLA. Bolin and Mako's influence reduces in S3 and S4. Opal, Lin and Suyin kinda take over after that. People keep trying to apply the ATLA formulas to TLOK, but TLOK evolved into its own thing and had a very different way of storytelling.
It's why I get bummed when people say Korra's team sucked. First of all, her "team" was FUCKING HUGE. It had rotating members. The actual story, not the promo material, put a lot more emphasis on Jinora, Tenzin, Asami and Lin than Mako and Bolin. I know ATLA got us used to the team members being of roughly the same age but if you guys are gonna count Suki into Gaang, then Tenzin, Jinora, Lin, Opal and Kai have all rightfully earned a position as Krew.