Different strokes for different folks is what I say. As Caine points out, all designs exist for a reason and have their perks. I just happen to prefer closed cabinets. But that same preference carries over to home theater speakers, car subwoofers and studio speakers in my case. To my ear, I just prefer the tighter response a woofer gives when there is pressure against the rear of the driver in a closed design. Not that there is anything wrong with the other designs. Your preferences may vary.
The Randall cab has Century's in it with Randall/Celestion stickers on the magnets. The easy way to tell is the wattage ratings. The Century's have 80 watt handling and the Century Vintage have 60 watts handling.
Can't help but wonder if there is something wrong with the cab you tried? Your review just doesn't sound like the sound of mine at all. I am familiar with the G-flex and have played through several over the years.
Did I mention my Randall cab is 35lbs?