High Imperial Roman army vs Late Roman army

[Robert Vermaat]

Well, only looking in your timeline, what happened in year 406 is something more than an evidence .... what the germanic invaders found or better did not find in Spain,it is something more than an evidence, in my opinion.
Look, reading the Notitia, In Spain there should have been 11 Auxilia Palatina and 5 legiones comitatenses under a Comes Hispaniarum, even half of this force probably would have been able to stop any invasion, so probably this force actually existed but sadly, ...... only on the paper.

Two things -
One, IF as you say troops had only exitsted on paper, Gaul would have been overrun by 400 or shortly after.
It wasn't.

Two, according to the ND, in 394 there would indeed have been 16 units. You say they were paper forces because they could not stop the invaders. I say, you forget the little fact that the area had been the scene of a civil war - it's in my timeline! Constantine III probably either disbanded these units (if they were pro-Honorius), or used them for the army he needed to invade Italy. Or Honorius pulled them out before that, fearing that scenario. Probably both.
That's more than nough reason to see them gone afterwards, leaving hardly any troops available to do anything else but defend Tarragonensis.