Power rack frame design

Hello, I'm working on a power rack project that I feel falls within the sidelines of timber framing more so than other woodworking disciplines, since it involves a wooden frame supporting dynamic loads of up to 600 lbs (in practice, the load will be less) and safety is implicated. I just finished designing it in Fusion 360 (first project with it) and I would like to get general input on its design.
It is primarily made of construction grade 4x4 boards and tenoned 2x3 braces. The joints are inspired by Chinese/Korean joinery found in framed Buddhist temples. I don’t intend to glue the joints so it can be disassembled if the need arises.

3D Model and dimensions:
https://yahoo145001.autodesk360.com/g/shares/SH56a43QTfd62c1cd968c716bdda211faf68

For those unfamiliar with Fusion 360’s browser interface, there’s an ‘Explode Model’ feature to disassemble the components and section analysis is there to cut through the model. Measure tool works the same way as in AutoCAD.
With that into consideration, is the design sound? I’m wondering more about the recesses supporting the middle beam taking too much material from the beams. Are parts of the ‘tenons’ on the top post joints too thin?

That's a cool idea. My worry would be racking of the little frame. There's really no lateral stability to it at all. I'm sure it's tricky to incorporate so that there's room for the bar. Could you incorporate a little bit a panel in the bottom to stiffen things up. I'm guessing that someone has made one out of wood before, so maybe some research into their findings would be valuable.

The little back frame is primarily there for supporting the large frame and for weight storage.

The Buff Dudes did a DIY power rack with no back frame and a higher center of gravity (my design tops at 80 inches for a low ceiling basement). They have used it for six years without any major issues. However their design uses steel ties, nails and screws which I want to avoid using. I'm more interested in using timber framing techniques to put the frame together, hence why I posted this project here.

What I'm wondering is if those joints that I've drawn are ok or if I should remove the top beam recesses to strength the post 'tenons' and simplify the joint like at the base of the posts. Two of them are 3.5/6 inches thick which leads me to believe they're the weak point in the design.

I think that your top joint is stronger than a standard mortise and tenon. If you extended the beam overhang a bit, and made it more like a true bridle joint. Then you have the end grain of the beam on two sides. Making that joint wedged (from above) might be a good idea. The joinery doesn't need to be crazy precise, it can be tightened up, and it can be disassembled.

I think that your top joint is stronger than a standard mortise and tenon. If you extended the beam overhang a bit, and made it more like a true bridle joint. Then you have the end grain of the beam on two sides. Making that joint wedged (from above) might be a good idea. The joinery doesn't need to be crazy precise, it can be tightened up, and it can be disassembled.