The old 75 gal
that I got used had no center brace. It has almost 1/2" thick glass & no bowing whatsoever when filled to the brim.
You can make yourself a center brace quite easily. Get a piece of glass maybe 3-4" wide & exactly the same length as the inside front/back distance of your tank. Silicone that to the center of your front & back panes at the top & you are done.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.