I totally agree that this stand looks underbuilt for the purpose, I'd have framed the vertical corners with 2x4s and either used a few triangle gussets or a diagonal 2x4 across the back. From the picture I'm not sure the cabinet is finished yet, as it is shown it's not a very good representation of a well engineered stand.
A good engineer understands that while a design may be strong enough on paper consumers demand a certain look or feel, extra reinforcements while often unnecessary are often added to make a product look more industrial, or give a sense of quality. As an example I worked with a folding table manufacturer as part of my senior project, the company we worked with uses a small triangle shaped bracket at the joint on one of the legs. They straight up told us that the triangle bracket was not structural at all, in fact the hole required to attach the bracket reduced the overall strength slightly, but it was needed to satisfy customers who thought the table didn't look "strong" without it. In this example the engineer added a piece of material that was tastefully sculpted to give the illusion of strength without adding unnecessary weight or cost to the product. The addition was made after an engineering analysis and testing, not an off the cuff attempt to solve a hypothetical problem.
I understand that carpenters are not engineers, I understand that framers are not engineers, I understand that most people who own a keyboard are not engineers, which is why I don't understand where people who aren't engineers get the idea that they are qualified to make an engineering assessment of a product based on a feeling. Would it surprise anyone if a stand that seemed flimsy when the tank was not filled with water could be very rigid when loaded with nearly a ton of water? It wouldn't surprise me.