I don't know why anyone would want to replace the factory installed Glock trigger. IMHO, it's a very good trigger.
You find that adding the Gen 3 trigger bar to your Gen 4 made it better. If so, in which way?Mine came installed with a dot connector. It currently has an NP3 coated OEM dot connector. The weight of the pull had nothing to do with the feel of that trigger vs the feel I have now. It's simply smoother in operation, with a crisp break, and reduced overtravel. I honestly care little about the weight of a trigger as opposed to how smoothly it operates. If anything I prefer at least 4-6 lbs of pull weight.
I can't speak for any other gen 4, or any other glock, really. I just know that mine has a sweet trigger on it. This particular G19.4 in its current state is a yummy yummy thing. I think the gen 3 bar has something to do with it and it was more than just a matter of polishing. The feel of the pull between the overwatch shoe and the Apex shoe isn't really much different, though i do like the feel of the aluminum trigger. The feel of both attached to the same gen 3 trigger bar in comparison to the stock trigger and trigger bar is vastly improved to what it was as far as I'm concerned.
Further food for thought. I have two versions of the P365 both 2021 models. A standard model that has a super smooth 5.10 to 5.12oz pull. The smoothness made me think it was super light or something. I've left that FCU be.
My XL on the other hand had a very gritty feeling trigger from the wall to the break and I've had the FCU apart on more than one occasion trying various things to smoothen it up. Otis dry lube seems to be doing the trick. My point is though, you can pick up two guns of the same model and get a different trigger pull due to the way tolerances stack, or just the right combination of two edges meeting.
I will add that yes.. there has been some debate about the effect of a gen 3 trigger bar in a gen 4 9mm platform. It was when I got the P365 that I decided I was willing to grab a gen 3 part for the 19 and see for myself. Unfortunately mine came with an aftermarket trigger shoe and I don't know how much they might be playing their part, but I like it.