ok i dont have a mage to test that specific focus, but here is a test using my SK.
summon spell used is Decaying Minion -
webtools/spell.php?id=9423That is the SKs T8 pet. With NO pet focus equipped it summons a lvl 73 pet. This will be sufficient lvl for this test. As your claim is the focus in question has a max lvl limit of 75, and hence is not effecting your t8 pet which is 79. (is it lvl 79 when summoned with no focus at all?
Now I summon again but this time with True Minion focus equipped -
webtools/spell.php?id=8512If you look at the spell data for this focus it has the max lvl limit of 70.
The new pet I summoned with True Minion is now lvl 79 instead of only 73, and has much better stats as well.