Well, looks to me that You need a different game
Have You played campaign? Surely one could use solely Scouts (providing enough cash, they're expensive) to win the game, but I dare to say that one would do
much better in campaign with several different types of units (I had roughly 1-2 of each foot and mounted skirmishers)
No offence, but from what I read it looks like You haven't given the game a spin yet, and played with mostly unpromoted, low level units (where scouts are actually looking nice, true). In my opinion knights are great (no Impetous near First Seneshal or they can have special perk to negate that), defence, movement and attack/charge can be raised as one prefers thanks to deliberately chosen perks. When they level up they are a serious threat.
Archers. Again, You can find perk for Youself if You look for it. Range, damage, defence... Upgraded archers in the forest beat *** out of crossbowmen, and besides, I wouldn't use archers to attack armored targets, rather as a cover and for wiping out enemy archers/flyers.
For Your question nr 5, if Your archer has "multiple support" perk then Yes, it can provide cover for every attack on neighbouring friendly unit, other than that it's only once. And to increase support on two tiles...
for #6
If Eagles are overpowered, wait for flyers from other races
And believe me, wussy archers in the forest can make a nice shish kebab from eagles
as for #7 I've written above. I like them as they are, especially that 1-2 units in Your army with "see invisibility" perk solves problem with ambushes.
And again, in #8 I disagree. Cavalry or heavy armored units are extremely vulnerable while river crossing, proper ambush on such unit results in large casaulties. That's why You need Light Infantry, support of Your archers (if unit goes into river, place archers behind their back and You can have "safe ford"), and of course special perks, with bonuses to river/swamp fighting, or fast crossing. Everything balanced, works fine.
So aside of some minor tweaks (I've noticed disappearing units too, and they hadn't had any special perks to do that!
) I'd say that it's better to concentrate on new campaigns, races, units, map editor and
random map generator, like in HoMM III.
My opinion only - play the game a bit more, it gets really nice, and even gold with most of units/cities done is quite possible