Hey, don't stomp on my joke, it's all I have...
Everything must be in context. Yes the one side takes its signal "later" than the other. But remember, electricity moves at the speed of light. (Please no arguments about electrons moving) And that can go all the way around the earth seven and a half times in a second. That means the delay for the lower side signal from the first is on the order of a billionth of a second. And at audio, that is about as close to exactly the same time as it gets. So your signal has to go through the inverting triode, then from that plate, it must go through the power tubes, the transformer and the NFB to get to the other triode. 15-20cm maybe?
US NAval Admiral Grace Hopper is famous for her nanoseconds. She used to demonstrate nanoseconds to her classes. She handed out a bunch of 30cm pieces of wire, one for each student. "Here are your nanoseconds." She went on "this is how far electricity goes in a nanosecond. One billionth of a second.
Hopper worked in the world of computing, and in that world, that nanosecond was a limiting factor in computer speed. If the memory was two feet away from the CPU, that computer would be slower than one with the memory only 6 inches from the CPU.
Grace Hopper was an interesting old bird, and sharp as a tack. I wish she was still with us, she could give a much livelier explanation of all this than I could.
We work in the world of guitar amps, and a nanosecond? Well, not so much of an issue.