You are right, SASless: Montgomery indeed ignored intelligence about the presence of SS Panzer divisions in the area. However, these badly-mauled formations had recently retreated from the Falaise Pocket and were more in regimental strength, than full-strength divisions. What was not grasped was the extraordinary ability of the German military to reinforce and re-equip these divisions, driven by Generalfeldmarshall Model.
Had the XXX Corps had been led by a commander with Patton's drive, rather than by Lt Gen Horrock, (who was in poor health, but a favourite of Monty's,) progress down the road to Arnhem might have been faster.
Diginagain: I wonder what was the Dutch Staff College DS solution was to the Nijmegen-Arnhem route?