A QTC of .5 is called transient perfect for a reason - it reproduces transients (ie with the least amount of ringing) the best of any alignment. It is the most accurate - but most people do not like it - it sounds a bit lean and thin. Higher QTC's are not as accurate - ringing more - but sound more real to most people. There is a brain interpreting this stuff - and that is precisely what you are ignoring.
No, I am not ignoring anything, I am explaining, if you care to listen.
All things being equal, a Q of 0.5 (0.577) will start rolling off sooner than a Q of 0.707 (which will give you flat, most extended frq response). So although you will have better performance in the time domain with 0.5, you will not in the frequency domain. That is the reason, that for a sealed box, people prefer the sound of a Q 0.707 alignment, it simply goes lower play louder and interact with the room better. These are all complex problems, that unfortunately cant be simplified to the level you are trying to portray here. I am glad you have Dickensons book, it is a good start (-;