I tried playing a little Fire Emblem Heroes (FEH!) since AC:PC makes me happy, and I played the first DS Fire Emblem game long ago. Nope.
Pro: Tactical combat is passable; small maps with slow movement, but has some challenge. Character art & voice acting is kinda sexy. Con: The “story” is incoherent nonsense, told thru very slow dialog boxes, and never allows you to make choices or kill enemies. Requires grinding fights over and over. Parties are limited to 4 chars, so by the time you have a tank, cavalry, archer, and magic, you have no flexibility to put in an optional char for levelling or a quest. Very few skill choices, no equipment or crafting. ★★☆☆☆ only because I like tac combat.
Compared to Final Fantasy Brave Exvius, which I played for a year: Pro: Main story was OK, had a few path options. Tons of new areas to fight thru (3-5 stages of 3 random fights) and then open up exploration: traditional FF dungeons & cities with secret areas. Characters are great, all the classic FF chars from 1-13, plus new chars. 5-char party plus an ally, plus summons. Tons of equipment & spell crafting choices, and easy to swap out for a specific fight. Con: Slightly aggressive IAP push, but it’s playable without. ★★★★☆ I only quit because after maybe 100-200 hours I had done all the things.
FEH isn’t significantly easier/more casual-friendly than FFBE, and it offers nothing much to a hardcore gamer.