Hence the tense change is merely a poorly considered pedagogic device in the construction of a traditional grammatical reference book. (I should have perhaps clarified this previously)
I'm not sure what the point is that you are trying to make, Fresco. Let me speculate a bit and you can correct me.
If it is that a traditional
[your italics] grammatical reference book suggests some measure of validity that is outside and unsupported by what the language actually dictates, then I would have to say that's preposterous and that that traditional grammatical reference book is of no value.
I say this because, if that same book cannot explain the difference between the two sentences in any better a fashion than to fall back to a nonexistent rule, then that book truly is trash.
Reviewing what you've written in this thread, you stated outright that the one with 'tense agreement' is better, stylistically.
You went on to say that both are grammatical. Again, I must ask; how can it be better to opt for a style that is artificial, ie. it does not exist in the English language, rather than opting for the meaning/nuance intended by the speaker/writer?
Isn't traditional grammar [is that the same as prescriptive grammar in your mind?] all about being concise?