I’ll consider making defender withdrawal optional via an XML setting in the next release. I understand it’s not to everyone's taste. You say you like the concept but not the execution, what do you mean by that? How else could it work?
Like when the defender withdraws, my attacker would fight against the next top defender it seems, so I ended up losing a lot more 99% fights. IMHO if the defender withdraws, the attacker should as well.
That's doesn't sound possible. Each AA unit can only intercept once per turn, so they must have had at least 20 AA units to intercept your 20 bombers.
Even if they did have 20 AA units, the stacking effect of the chance to intercept only counts units that haven't already intercepted, so the chance to intercept decreases the more bombers that have already been intercepted. Also, bombers have a 15% chance to evade interception regardless. To have all 20 bombers intercepted would be quite unlucky.
In general though, if the AI has lots of AA units in a city then it's not usually a good idea to bomb it anymore. The point of the stacking code was to make AA units a worthwhile defense against this, so you will have to use other tactics. Try sending more ground forces and artillery instead, or bombarding from the sea if possible. The jet/stealth bombers can be more useful here since they have higher evasion chances. If you do decide to bomb a city with a lot of AA units, expect a high intercept rate, it's best to do all the bombing in one turn right before you attack to make it worthwhile.
I think he had destroyers and machine guns too, but I didn't count those.
The problem I see is AA is too good compared to fighters, since you can pile an unlimited amount per city as opposed to 8 fighters, and fighters take damage and can be shot down, AAs take no damage from interception and defends against ground units too.
P.S. another thing I noticed is I can build both ironclad cruiser and destroyer escort at the same time. Previously the latter obsoletes the former