First off, I am in no manner complaining.
I like your design and have no intention of abandoning them.
This isn't because of them per-se, it is because a framing member has been removed.
It would be the same with almost any method that removes this piece I'd think.
I checked the framework for rigidity not only because I removed the front center bar, but because I installed aluminum corners and tees at the same time.
I placed the printer on the floor rug and manipulated the top-most frame pieces.
Front-rear, on either side, no change from before was observed.
Rear left-right, no change from before.
Front left-right, it is now quite plainly more compliant than the rear left-right.
This makes sense to me because a framing member that acted as a center tie has been removed along with the plates that braced it to the verticals.
I plan to correct this situation by adding 12"-14" long diagonal braces from around the middle of the bottom front rail to the left and right front uprights.
I will do the same from the middle of the bottom side rails to the rear uprights.
I may even add smaller ones (so as not to restrict vertical access for the filament feed) to the top corners.
I agree that the loss of stiffness does not affect alignment in a static sense.
However my suspicion is that with the print head carriage thrashing about as violently as it does, the frame may flex too much and cause the build plate to oscillate.
Even before all of this I had already planned to add braces because of artifacts I am seeing in printed vertical walls that indicate frame flexing to me.
My X and Y belts are tight, carriage pieces are tight, sliders are tight, and so forth. They are not the problem.
I can actually feel the framework flexing as it is printing.
The large side plates shown in the "tall" printer thread ("massive ft-stein") are a superb idea IMHO.
Without them the framework would flail about like cooked spagetti.
I am going to try my diagonals first before resorting to that though.
Anyway, try comparing the left-right compliance of the front of the frame versus the rear on yours if you haven't already added diagonals.
You might be surprised.