I personally missed the Gargoyle maze on first pt and also missed a bit of xp towards level 8, but you can also level up during Alexander fight even when you don't kill an enemy but the drillworm.
Honestly tho just leveling from 7 to 8 is not gonna make Alex that much easier, rather try to mprove your strategy.
For me soloing the fight was really hard until I realized every Magister just focuses the Drillworm once it shows.
You can do so much damage in that time and ofc ol wormy will do damage, too.
