You aren't really being level headed at all since you are focusing on one primary point actually. A level headed individual takes a unilateral and unbiased approach to come to a distinct conclusion. Your primary points actually dictate you have a very one sided view on the subject and is shown by how eagerly you dismiss apposing views on it.
Your analogy is worse than mine actually. Trucks serve far different purposes from a Ferrari. If you wanted to use vehicles to express an analogy of relic/myth/emps it would be more akin to a base model of a car to the same model with all the bells and whistles, the only difference being that emp/myth/relics are just different makes (chevy/ford/dodge). Each offering something different, bells and whistles wise, to accommodate being useful over one another. Anyway, moving away from the analogies for now.
The test server is in essence a big play ground with a plethora of toys at an individuals grasp. Relic/emp/mythic weapons would be no more different than the fact SE is planning to give invincibility for testing purpose later on in the terms of "play things." The biggest functional difference between this being that on Live servers (non-test servers) the weapons will still exist where as the invincibility won't. Allowing people the toys to play with doesn't necessarily negate their ability to test the actual content of the game either.
I have both a relic (mandau) and an emp (almace) but you know what? They don't really see much use on the test server because there isn't enough like minded people on the server at a given time to fully test the content being added when it comes to WoE or VWNM. The purpose of a test server is for an individual to test it anyway, and everyway, possible to be sure that one minor thing doesn't break an intended outcome of the content. You've also constantly dismissed the fact that the weapons are undergoing constant increases in their functions, from base damage, to additional stats, to additional hidden effects. Dat mining sources show that there is possibly a very big change coming to relic/mythic/emps in what is being called "afterglow/aftercircle." Depending on how this effect works, it could possibly be unbalancing in content. In most cases this never gets the chance to be tested by those with the weapons because...well they need help or high quantities of an item to upgrade it on the test server. There is no simple way to upgrade it to the next stage on the test server, thus "just let the holders of the weapons find out for you" becomes a moot point.
The test server was made to test things, not limit an individual or tell them to use what they have. If this were the case, there wouldn't be moogles to give you better than what you have already (AF3+2, WoE, Rare/EX weapons, Salvage gear, Abjuration+1 gear, etc). Once again, the weapons themselves are going under changes from 95-99, thus are part of the test content. The weapons will not give anymore of an advantage to an individual than the proposed invincibility they plan to add to the test server. The opportunity to have a higher population for group related testing outweighs any advantages the weapons may give since it is better than not having the population to test content with at all. The only aspect of your debate I see is "They are toys and unnecessary" and that is true, but everything the GM moogle offers can be given the same point making your entire objection to allowing an individual to have access to the weapons moot on this basis alone.