It's because, as per usual, they are overplaying the competence of the HP Wizards by leaps and bounds(Like they always do) as well as their magical ability which is no different than how people do Overlord.
I already went on a tear over how bad Ministry of Magic Wizards are(They literally went all in on the orders of a certain item made by Fred and George Weasley because they made actual good Protection Charms) but Aurors are not made out to be any superior to even a typical Death Eater(They tend to forget Bellatrix LeStrange is basically the top of top tiers for Death Eaters, she is NOT their average considering she took down multiple Auror-tier opponents). Hell, Molly only defeated her by literally amping her Spell to the point it legit stopped her heart through sheer anger and rage.
So in laymen's terms, most HP Wizards and Death Eaters are hilariously incompetent with only a few being exceptional for not being dunces or believing they are better than the "Muggles"(Which even the good guys believe). This is again missing the fact that J.K. Rowling has stated in several points and we literally had Fantastic Beast 2 show us that the Wizarding World wouldn't stand a chance against WW2 Weaponry, the fuck chance they'll do against modern day weaponry?