Well, I guess that's just the equipment he had available at the time. Back in those days there wasn't much available in the way of audio recording equipment. Nobody made mixing consoles and such. You had to make stuff yourself. I agree with you, but if you listen to the records from that era on Atlantic, that's just how they sounded. Kind of like how those old Motown records are sonically not that great, but later on, when they sold records, they made money and updated their gear.
I've read that Rudy Van Gelder modified or built much of his recording equipment, and treated the equipment and his methods with more secrecy than nuclear missile plans. I suppose that's what separated him from the rest.
Yes, and that's why everyone in the jazz community wanted to use him. Atlantic, back in the late 50s and early 60s, was just a startup label, not the behemoth it later became. I probably have better recording technology in my cell phone than Tom Dowd had at his disposal back then.
Also, RVG only had to record jazz. Atlantic recorded all kinds of music. The techniques for recording different types of music are different.