Nope.  We're not.  There could be some technical reason why FE can only support ~18 units on the screen at the same time.  That would seem to me to be an enormous flaw in their game engine, but it's certainly possible.

A few major differences here...

First, in both Chess and Stratego, you only move ONE PIECE A TURN.  In FE, you move every single piece, every turn.  Therefore, the length of your turns increases linearly with the amount of units.

Second, Chess and Stratego are all about the "tactical" battle, it composes the entire game.  But in FE, a battle is just a small part of the overall campaign.  I don't think you want to spend 40 minutes in every single tactical battle because you will never finish a game and will probably get bored.

Third, Chess and Stratego are completely balanced at the start of each "battle."  The tactical battle system in FE is not balanced by design.  In any one tactical battle, you may be significantly overpowered, underpowered, or around even...all depending on what's going on in the campaign map.  While playing a long-term balanced battle may be enjoyable...it will be just painful to have to spend 10 minutes giving units orders in a battle that you know you are going to win.  Think about how many battles you engage in that are actually "balanced" at the start...

So you're going to round up 20 heroes?  More power to you!  I'm pretty sure that stack should be absolutely epic and should not be simply countered by a comparable stack of 20 mundane units.

I'm pretty sure that's how FE's tactical battles are.  The innovation of initiative allowing units to skip ahead of others.  WoM was each side moves all its pieces and then the other side does, but they got rid of that system.

Which is why the autocalc button is there.

edit: I'm pretty sure.

It's not the same.  In Chess, you have a turn, you can decide whatever unit to move in that turn that you want.  Giving you lots of strategic options.

In FE, your UNIT gets a turn and you can move it.  That's it, you can only move the unit when its turn comes up.  It essentially means that in order for a unit to move twice, you have to wait (on average) for every other unit on the board to move in between moves.  It can take forever.

In contrast, in Chess I could move the same pawn in two consecutive turns.

If the tactical battle system is so lengthy that you are forced to autocalc all but the most potentially interesting tactical battles...then I don't really see that as a good thing.

Sometimes you want to drive an easy tactical battle just to conserve resources or optimize.

OK.  But this is a new objection, quite different from the one in your post and to which I was replying.  Yes, chess and FE are not exactly the same.

I understand that theoretically, you might end up waiting a long time between the moves for one particular piece.  but while you're waiting, all the other pieces are moving and doing interesting things.  The game is not made more boring because there are more pieces.  Yes, it might take a couple turns before your unit gets close enough to do damage, but the same is true in many games.

This is not responding to what I said.  My point was that suggesting that adding units might make some tactical battles boring is not a valid criticism.  There's already an autocalc feature which suggests that even the developers recognized that the tactical battles are not always going to be interesting. 

The truth is that uninteresting, lopsided battles are a given in turn-based tactical combat.  The number of units involved in the uninteresting, lopsided battles is irrelevant.  Instead of taking 2 minutes to pointlessly march your units over and wack the wolfs, it takes 2.5 minutes, the horror!  If you want to "drive an easy tactical battle just to conserve resources or optimize" then that's what you want to do.

And you want to talk about boring: in the current game, take your stack of doom and go and fight 3+ stacks of enemy units on the same turn then attack the city that those stacks were marching out of.  The same exact battle fought four times!  Just in case you didn't get enough excitement the first three times.  That's how battles work in the end-game currently, because you can generate far more units than can be in a stack.