well, attacking with a stack of mithril champ is not the same as attacking with a stack of bronze warriors..
and honestly, you can't really take cities when you only have longbows...
and you are not speaking about normal civs: you plays Kurios... when you have centaurs you don't need champions. I agree.
but the other civs don't have centaurs, and Horse-archers/chariots are not as interesting.
sure, champions suck a bit, but they are still important.
I agree with first strikes...but you still need str or combat to make those first strike count.
basically, FS allow you to "try to hit" a few times before the ennemy retaliate.
however, the chance to hit, and the damage you do depends on your total combat value difference (str modified by combat % and defense %)
so a 6str attacking HA with FS, with flanking and FS maxed out, have very few chances to damage a mithril champion (10str), with combat 3 (+60%) (much less xp than your HA), fortified (+25%) in a walled city (+20%) : 20.5 str or something:
at 6 vs 20.5, your hit chances per hit-try is very low, and your hit-damage per obtained hit is also low.
your only chance to damage a bit this champion is if you have 3-4 times the number of HA. and then you will still need some attacking units.
while on the reverse, that champion (10str +60%) will one-shot your 6str HA.
further,
in your comparison you explain that champs are bad .... in defense..
but the true moment where champion shine is in mixed offense/defense:
only 1 tech tree to get a decent defense, and a powerful attack.
it further levels up with your tech.
6str unit is ok, 7 with bronze, 8 with iron... you are decent for early-mid to mid game.
then late game... 10str with mithril: that is really really decent.
howerver you are right, they are not the best units, but that is mostly that their High STR and late-game utility is not really compensating the 1 mvt.
when you go check in Magister IIRC he added 1 free promotion to champions to give them a bit more shine ^^
