In pure gameplay terms;
By dropping the Paladin levels you'd be gimping your own melee damage in scenarios where you may want to burst down an NPC quickly and by doing so you'd be shifting your arsenal balance drastically towards spells (like Magic Missiles) rather than being equally deadly with both the blade and spells.
Which means any NPC with Counterspell would entirely restrict you to just pure melee (which still does decent damage), but you'd waste several turns hunting them down due to lack of melee burst damage instead of just smacking them once to get them out of the fight (as the video above evidently shows how both casters got knocked out in a single turn).
That's why the Paladin is useful so she doesn't become a one-trick pony that's easily shut down by a single trivial spell, instead she's equally deadly with both melee and spells. She always has options for every scenario.
But as I keep saying this is a roleplay build I carefully crafted for myself to fully embody Eilistraee's lore, that just happens to also be powerful and versatile enough to solo Honour Mode. Without the Paladin, solo Honour Mode is out of the question and if one is not interested in the roleplay aspects of it, then there's really no point in even trying to replicate it.
