Tthat's what I did initialy... Then I got feedback.Yea, I think it depends on the map what you want to change that can change the dynamic of the map.
Chapter 14 got me thinking that you really don't want to give the player too many additional starting units that map on easy/normal, but weaken the enemy snowball potential in their bases/income (or the reverse where the player gets more reinforcements later to respond to the enemies), otherwise you can just build a wall using those additional expendable units you start with and then have Chloe finish the main objective and win that map.
You see you and me are probably tryharder kinda minmaxing turn etc in some way.
But when someone that isn't good at strategy game or just want to play without thinking, they don't really focus on taking good trade necessarily, so the fact that the player has no base and the enemy does, mean that in this mission to survive you have to brainwash more unit than you loose on average. If you add to that the fact that Saki is a monster on the battlefield (especialy when she had bonus def because on a forest) you can easily have the player loosing initial forces and have trouble getting back into the game. The is especialy true if your hero like Fionne get hurt (which is more likely to happen in this mission than other because Saki is super tanky, which mean you have to choose between brainwash a unit or get her to hp1 to neutralize her. Which mean you're likekly to have surviving threat.)
Of course the easier mode are kinda abusable in this mission but honestly, is it bad? I mean if one of the mission can be completed in 4 turn on non hard difficulty, I'm fine with it. It's unlikely that it happens by chance on normal (maybe on easy though), so as long as the player made a concious decision about it I think it's only fair they're rewarded.
They didn't choose hard so it doesn't have to be hard.
Of course if all mission would end this way it would be a problem, but I think it's fine here.
Edit : The way I think it is, when I'm designing difficulty, it's like if I'm trying to please totaly different persons.
Hard:If someone play hard I suspect they want to have make an effort to win a level, so I do my best do make the game at least somewhat hard.
Normal: I don't think people playing on normal are looking for difficulty, you just want to make it hard enough for the battle to make sense (if you send your archer on the front or do stupid things like that you'll loose, but aside from that you shouldn't need hard concept like walling (except on the defense map but then it's explained in a tooltip that only appear when people select normal/easy difficulty)).
Easy: The game should be easy, but also probably a bit quicker than in normal. So I don't give stats boost because I think it would be bad immersion wise, but I try to ensure that it is really easy to win the missions (and not too hard to have every named character survive)