If you think about it, pausing at the bottom is tipping the ratio of chest/tricep more to the chest because you are holding the time longer on the chest.Basically I think the biggest values from slightly slower eccentrics (with a measurable dead stop) come from two things.
First, they help to standardize what a rep looks like in a particular set. This is important when trying to measure progressive resistance. Call bullshit reps what they are, cheat, partial etc.
Second is all the things that we mostly look at as physiotherapy but improve hypertrophy outcomes by many means which add up-
Im taking that same idea more extreme, just cut the triceps out, I have 4-5 moves for the tricep alone each week. repeated at least two days.....
I don't think there is a bullshit rep based on ROM or speed if you have a goal, and you achieve the goal.
If you are total newb, and your literally just trying to ego lift, break records, convince yourself your strong thats a very different situation for a shallow rep.
Like you said you seen pros do only the top part of the rep, and avoid the stretch.
Dips are perfect example of this.
I can do dips on chest day and make it a chest move, by staying low enough I dont feel tricep.
I can also do a super shallow top half, and dont go any lower when I feel my chest start to take the load.
You are basically taking a compound lift, and emphasizing a target muscle, kind of making it more isolated.
This leads you down a road of doing twice as many moves, or more to get your full body. But it also allows you to custom tailor the stimulus, and ends up maximizing your overall gains. And this is how you get the point where you can start to target weak spots, and actually sculpt your body. In my case it allowed me to unlock chest growth which I just never figured out before this.