I agree that that 2 Kings 17:7-23 is discussing the moral failings and their consequences of Judah and Israel. Further, it is clear that v24-28 is discussing the mixed multitude of people that had been imported to inhabit the deposed land, namely, (v24) peoples from Babylon, Assyria, Cuthah, Avva, Hamath, and Sephar-vaim. All these people had their own gods and their associated religion.
However, the lions sent by God resulted in some priests being sent to the land to teach people how to serve and fear the LORD.
The result of this was mixed religion consisting of some of the practices of the mixed multitude plus the fear of the LORD (v31, 32). v33 continues to discuss the mixed religion and practices of these mixed people, "they feared the LORD AND served other gods".
v34 is significant - in serving both the LORD and other gods, they do not serve the LORD at all. That is, religious practices, liturgies and chants that incorporate the name of the true God does not constitute true service to that true God because that service requires exclusive service to the LORD (Ex 20:1-3, Deut 6:13, 10:12, 20, 13:4, Josh 24:14, 1 Sam 7:3, 12:24, etc).
Thus, v33 concludes that because they did according to their earlier customs, they did not [really] fear the LORD, presumably because if they did then all the other gods would have been put away.
Therefore, I see v33 & 34 as continuing to discuss the same mixed multitude and mixed religious practices discussed in the verses 24-31. Ellicott reaches the same conclusion:
(33) They feared . . . gods.--Literally, Jehovah were they fearing,
and their own gods were they serving. The verse recapitulates 28-32. …
(34) They do after the former manners.--They still keep up the
religious customs of the first colonists. They fear not the
Lord.--They fear Him not in the sense of a right fear; they do not
honour Him in the way He has prescribed in the Torah. The LXX. omits
both nots in this verse. After their statutes, or after their
ordinances.--The writer here thinks of the remnant of the Ten Tribes
who amalgamated with the new settlers (2Kings 23:19; 2Chronicles 34:6;
2Chronicles 34:9; 2Chronicles 34:33; John 4:12).