Synonym or equal phrase to "merely philosophical"

Solution 1:

You might just avoid the construction: "Arguments over the purpose of the account are irrelevant", or "Arguments over the purpose of the account are beside the point". Aside from being inoffensive, I think either of those more explicitly makes your point.

You might even use something like "My argument [position/thesis/whatever else] does not depend on the purpose of the account."

Let me add that if your audience includes many philosophers, especially philosophers in the mainstream Anglo-American tradition (what gets called "analytic philosophy"), this sort of plodding explicitness is exactly the style that they're looking for.

Solution 2:

You might be looking for academic.

academic interest:

The questions are not only of academic interest, but ...

rendered academic:

The question of whether he was killed using an axe or a machete is rendered purely academic ...

academic pursuit:

Interest in etymology used to be a purely academic pursuit ...

Solution 3:

To avoid terms like merely philosophical, purely academic, and a scholastic exercise, consider of no practical value, of no bearing, or of no consequence. The following example illustrates several of these terms: "Arguments over the purpose of the account may be of interest to inquiring minds, but have no practical value and no bearing on further developments of the topic. For this study they are of no consequence."