Sheesh
Fun game, liked it, constructive critism to follow in a second. I look foward to the sequel, dont care if people say its a ripoff, its fun.
Mirroring alot of what others have said, what is the advanced tier units in their current form? Due to the lack of upgrades your basic units outpace the higher tier ones. Heck even Peasants are more useful than some of the upper tier units just due to cost::use ratio.
I need to have a reason to move up in the various tiers. A single unit that gets instagibbed or due to lack of upgrades has less health than previous tiered units is where the problem lies.
Should the lower end tiers still have a use? Sure, should they be the best in the game? No... If someone wants to go burn 40-50 game days to get an army of full tier 3 units, they should have units that are significantly more powerful than the previous. Will it effect game difficulty? Well yeah, but this has RPG elements and the basic rule of RPGs are "if you cant kill it, go level up more".
Chapter 16 was a horribly balanced fight. I don't know if there was supposed to be some secret konami code to make it doable with ease, but it was the only fight that took me more than 1 attempt to beat... In fact it took well over 10 attempts where as the last fight was again, a 1 shot. This seemed to be due to a bug(?) in how the games AI works, or perhaps just an oversight when you set things up. Once enemy units are in range of your flagcarrier they're gonna turn and blow him up. It seemed like on chapter 16 that there was a hard stop on the enemy units, where they would no longer get pushed back. This was before the victory line so you had to keep telling your troops to push ahead and hope you got lucky and the AI would keep smacking your meatshields instead.
TLDR: Make every unit have upgrade features, even if it means the top tier units are over powered. Make it cost a fair amount to get them there though. No more missions like chapter 16.