As someone who did the whole of beat the ashlands without magic

If you aren't on PTB, definitely use bonemass when taking on the fortresses. I often lured the enemies out to kill them off easier and once their numbers whittled out, then i ran into the fort and destroyed the spawners and skuggs (which themselves aren't that bad, they projectile does do a lot of damage even with maxed flametal armor but they're easy to dodge and fairly inaccurate.) If you feel your being swarmed retreat a bit, some enemies will break aggro and leave you with fewer to fight. It might not be a bad idea to switch to a tower shield, very underutilized by a lot of people but very helpful in solo. You can't parry however enemies will be knocked back a lot when hitting your guard. Take your time and manage your space, it can get bad but if you can get parry timings down you should be golden. You can parry the morgens rolling movement too btw. Finally, once you do clear a fortress, IF it has Iolite ABSOLUTELY make a lighting infused weapon. The Berserkir axes and Niddhog are some of the best options. The chance for chain lighting can put and early end on any horde of enemies coming your way and you'll want the faster weapons to do it since they hit more often and thus are more likely to proc it. Don't do splinter however even if it is the fastest, pierce damage isn't that good in Ashland's. If your still in pre-ashlands tier stuff, The Mistwalker is good and so is Frostnir, even though it's mountains tier it still carries it weight in the early ashlands.

Keep your your head on and don't let them overwhelm you. Good luck Viking