I don't even know how they're going to extend the series.. I thought dealing with the blood bender was the peak of the story.. However, they need better story telling in the new chapters, and bending on the level of the Last Airbender because LoK was a disappointment..
honestly i expected amon to be a non bender who learned how to bend chi from the lion-turtle like aang did in atla.
As for power level differences. Everyone who was someone in atla were masters at something/bending (toph was the best earthbender, aang the best/only airbender, katara was a master by end of part 1, and every one in the royal fam was prodigies)
in lok bolin and mako are your average everyday benders, and korra has to restrict herself not to ruin the environment as seen in ep 1-2.
Iroh 2/Lin/Tenzin having learned from the masters are naturally better. (irohman can fly, spiderlin can metalbend, tenzin is boss)