Especially if they multiclass to get those higher level spell slots after a few levels of the base class (or go back & forth). Normally the idea of an EK/AT getting a spell like the 3rd-5th level spells (which I don't think are even available) would be an absurd stretch, but because because of how the dragonmark spells are justified in lore it feels like the
"if you have a spellcasting or pact magic class feature, the spells of the mark of x feature are added to the spell list of your spellcasting class" should be errata'd to be exempt from this bit of the multiclassing thing "i
f you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. " with houserule or an
errata. That also solves some of the "shouldn't be forced to take a spellcasting class" complaints made by
@doctorbadwolf & others I've seen since instead of being an EK, a denieth mark of sentinel human could take other paths than just sticking to one class like a few levels in a half or third caster class & half as many in a fll caster class