Zaheer is the leader of the Red Lotus and it's airbending member. Despite his lack of experience with airbending, his combat mastery, intelligence, and ruthless dedication to his cause make him an opponent to be feared.
While airbending isn't the best element for putting people down quickly, Zaheer's striking power is still quite respectable:
While Zaheer is not your traditional airbending master, he's not an unskilled novice either, having studied airbending to teach it to Korra, and being a high level prodigy.
While Zaheer was formidable even before unlocking this, he reached a whole new level when he discovered the power of flight.
Speed and Agility
Speed and agility are two things Zaheer excels at, and he is firmly in the upper echelon of speed in the avatarverse.
Tonraq himself is respectably fast, making this quite impressive.
Strength, Durability, and H2H
In addition to being very fast, Zaheer is also quite physically imposing, fitting for someone who used to be a nonbending martial artist.
Strength and H2H:
Durability and Recovery:
Ghazan is the earthbending master of the Red Lotus, and a master lavabender. In fact, he essentially invented it (some avatars did it before him, but they bent pre-existing lava, rather than create their own). In terms of sheer destructive output, Ghazan right near the top of the avatarverse.
While Ghazan isn't an incredible pure earthbender, he's still quite respectable, especially in the field of boulder negation.
In terms of sheer scale, lavabending is hard to beat, especially because of how it spreads out over time.
Speed and Agility
While he's not on the level of his teammates Zaheer and Ming Hua, Ghazan is still respectably fast and agile.
Ghazan doesn't have a ton of durability feats (although he had some good ones against Mako and Bolin), however he is exactly as durable as Zaheer (who I posted feats for above) and Ming Hua, based on this feat:
While he only had a few fights, his track record against named opponents was respectable.