Whoa there. In Lunatic, and Lunatic+, mode your options to grind are significantly decreased. Risen battles are a lot tougher, like end-game to post end-game tough, and give way less EXP. Summoning enemies to fight via spotpass gave very little exp as well, like 1EXP per kill lol. The only reliable to way to grind in those modes is through DLC. For Normal mode and Hard mode though it doesn't matter because those modes are significantly easier.
You are also wrong about grinding in past FE games. Sacred Stones had the tower and ruins where you fought monsters and where primarily used for grinding, along with arenas for some of the maps. Shadow Dragon had arenas for certain maps. The Telius series were the ones with the least grinding options but they had BEXP instead which served a simmilar, more limited, purpose. I know FE7 has arenas to, but I'm not sure if anything else (I have yet to play it yet), and I have yet to play any of the Japanese only FEs.
But there was always some kind of effective way of grinding in the ones I've played, if you know what you are doing.