it's shit.
I say this as a HHM/fe6 hard vet, any of the lunatic modes on the 'open world' campaigns (awakening, birthright, revelations) are fucking shit. Same as a regular playthrough but you have to grind like a motherfucker (or exploit DLC, which is more-or-less encouraged) because everything oneshots you in the first few chapters.
It's harder, sure, but at the expense of actual fire emblem mechanics. For one thing, because of how pair-up bonuses work, it's much smarter to grind up a handful (2-4) of godlike super-units and let them steamroll everything. Kills the whole 'army building' thing. Like >>13953970 said it's the same basic game just everything has inflated stats and bullshit skills, and you can't out-strategise it- you just have to grind.
Can't speak for CQ lunatic, but it's better, although a bunch of the chapters you more-or-less have to cheese with flier rescues and movement refreshers, or recruiting specific enemy units with certain skill setups