How did you strengthen the trigger bar?
Random thoughts:
If you run a lighter plunger spring you can improve the trigger pull, but how do you know if the plunger is returning to its home position quickly and blocking the striker? And does that even matter?
If you are using a 6lb striker spring, wouldn’t that add to the resistance on the trigger bar making it tend to flex more? What made you want to go up in striker spring weight? Did you polish the striker tail?
Would using an aftermarket (Ghost) connector also lessen the resistance on the trigger bar making it flex less?
Honestly, I haven't kept up with the changes that Glock has gone through from one generation to the next. I do not know what changes have been made to trigger bars, nor do I know what, if any, changes were made to accommodate the slim line of Glocks. I only know that my trigger bar flexes, even when using a 5lb striker spring. I compared my trigger bar to that of a G26, yesterday at the range and noticed that the trigger bar differed from mine in that it has one large and deep valley in the bar to lend to the rigidity of the bar. My bar has two small and shallow valleys, which are possibly inadequate, and flex is still occurring.
Let me answer your questions in order.
I strengthened the trigger bar by milling a piece of aluminum to a thickness about equivalent to that of little more than half the thickness of the trigger bar. I then cut it to match the contour of the trigger and I used jb weld to affix it to the trigger bar between the bar and the frame. The rear of the bar at the sear still flexes a tad when you hit the overtravel stop, but very slightly. The flex in the bar between the trigger and the 90* bend that leads to the cruciform is gone. In hind sight, I think I made the job harder that I had to, but the idea struck me in the middle of the night and I used what I had. What I should have done was acquire a small rod of some sort of steel, maybe spring steel, put two 90 degree bends in it at the ends, pop two holes in the trigger bar to fit the bends in the rod and adhere that to the trigger bar in between the two valleys on the side opposite the frame. This would have been cleaner. When I can get around to it, I'll give it a try. I have a spare trigger bar to use as a guinea pig. To date I have close to 1000 rounds through the gun and all is good and solid.
To the rest of your questions, the trigger bar (in it's stock form) flexes. The flex is caused by the resistance of the striker spring and there's nothing you can do to stop it from happening. As far as my appreciation of the how the connector works goes, getting a ghost connector may or may not help. I'm running a Glock 3.5lb (minus) connector and have been the whole time.
I was able to see what was going on inside of my gun as I manipulated it and dry fired it by using a fiber optic camera shoved up the mag well. I used Gorilla duct tape to hold it in place and commenced to becoming a mad scientist. This gives a good view of what's going on with the plunger and the trigger bar while the action is doing its thing. I also confirmed the working of the safety plunger by placing the camera in the striker channel with the striker removed, but this was more about setting the over travel stop to insure that the plunger safety was completely disengaging.
I'll snap a pic of the mod on the trigger bar when I unpack. I just got back from the range. I'll edit and update this post in a bit.
For those of you with all of the comments regarding YOUR number of Glocks all being stock and perfect, unless you have or have had a 43, 43X or 48, none of this applies. As far as I know.
*EDIT*
Here are the links to the trigger bar mod that I did.
https://photos.app.goo.gl/yTxH6q4m7uweUYq8A
https://photos.app.goo.gl/U1VbNiwbPSiRVTKW7
https://photos.app.goo.gl/RTxxLsNsDS4QqxiHA
I hope you can see them. Everything is so shiny.
