Since you mentioned my level I should share my general formula I tend to adhere to:
My levels usually have 4 sections, two per half (or 1.33 per third or 1 per quarter, depending on how many checkpoints are necessary).
The 1st is a little introduction to the majority of stuff I wanna throw at the player later.
The 2nd section presents a mix of these elements in a new context (vertical section, underwater section, one-screen gauntlets) or is sometimes omitted for some other reason (Bold and Brash: having the checkpoint before the autoscroller).
The 3rd returns to the formula of the 1st but does more tricky things in which I sometimes foreshadow setups from the 4th section in a more relaxed scenario.
The 4th section can be anything, as long as it signals to the player "yo, we're about to end the level". Usually this section is higher-tension throughout and calms down a screen or two before the end. (I noticed you did this in your most recent level by deploying a dark foreground overlay)
The section structure is absolutely not rigid and while typing this I noticed a few dozen examples in my recent levels (unpublished) where I betray it. Sometimes the 4th section is a few-screen subsection of the 2nd half's main section, sometimes I only have three sections plus a little one-screen gimmick, and sometimes, if the situation calls for it, I also make just one really wide section that includes everything and has some visual shifts to indicate progress.
What I hope to have conveyed somewhere in the midst of this is that it might be useful to give every section a distinct purpose, so that the player feels that they're advancing towards a goal. That's easier to do with a low section count than a high section count, I feel.
Of course, expectations can be subverted. Checkpoint placement is also a double-edged sword in terms of progression since it can only signal to the player how long a level will be if it's consistent throughout. Or you could use the fact that many sections don't signal progress and build a literal ten-section one-screen-maze the player has to figure out.
Anyway sorry for riding this point for so long. I hope some of it makes sense.