Ahh sorry, I haven’t been very involved in the game lately, but I’ll still do my best to help with what I can.
I haven’t read @FishDreams complete summary, but I trust it’s on point. 
Anyway, I’ll give you some advice quick from what I see. If you have anymore questions, or need anything else, feel free to ask.
So, we’re talking war/regular defense team? Alright
Red: Wilbur is maxed, which is awesome, but he’s no good to have on defense ever unless he’s your only option; giving spirit link to the opponent can be more of an advantage than a disadvantage for the other team. Scarlett is fine as a wing hero if you don’t have many fasts; she’s too squishy to flank. Colen can be pretty brutal on defense for a 4*, but Azlar is basically the bigger and badder version of him. So if we’re just talking defense, Azlar would be a beast, but needs to flank or tank to have any hope of going off (same applies to any slows unless they’re Alby/MN). Gormek is alright on defense, but has so many HP points, so he’ll inflate your war score if he’s in your war defense setup. I’d use Scarlett over Kelile on defense, but Kelile would have better survivability if you went with her instead.
Blue: Kiril is a solid supporting hero to have on defense; healing and attack and defense boost are amazing. Though, he should be in left flank, doesn’t make a very good tank, and might not go off in time in the wings. Richard is also a beast on defense; a great tank or flank hero. Sonya is nice for the dispel, so if you have no dispellers on defense, she should go in the left wing. Thorne, well we’re gonna ignore him for now.
Green: Caedmon is maxed, so he’d be better to have in the left wing over Sonya for the dispel. Plus, he hits harder than she does. Melendor is too squishy on defense (imo). Little John hits like a truck, but he’s slow, so you won’t want more than two slows on your defense teams, so just be aware. He’s also super squishy, so easy to get rid of before he goes off. Do like him though. Kashhrek is going to be the best 4* tank you will find, so until you have 5* at 4T, I’d be using and leveling him as your tank. That would mean not using Caedmon in the wings (to never double your tank color), but you can do Sonya when she’s ready. I’m going to ignore Skittleskull here, doesn’t add much to defense. Gadeirus has a cool buff and all, but ultimately doesn’t help out too much defensively with slow mana and a weak attack. The buff is his best quality, which is better on offense.
Yellow: Li Xiu is probably the best defensive yellow 4*, so I’d be putting her as flank or tank to cut mana. Wu Kong isn’t great for defense, so leave him out. Chao, you could use, if you need another fast mana hitter in the wings instead. Justice makes another beast of a tank. Is slow, but that blind can be brutal, and she’s got a ton of defense. Another good candidate for tank. Danza is too unpredictable. Hu Tao is too slow, like a worse version of Justice. Musashi is fast, so he’s excellent in the wings, and his attack stat is pretty high too. Not very high of defense, so I wouldn’t ever have him flank.
Purple: Cyprian is alright on defense, but I’m not a huge fan of counterattack since it can be so easily dispelled. Still, could make an alright flank hero since he’s already almost maxed. Sabina is too squishy for defense. Domitia is alright on defense, the holy buff is nice, but she’s not amazing at it. Still, she’s good. Ameonna isn’t all that great on defense; the ghost thing is cool, and can be a little annoying, but usually doesn’t help or make a difference at all. Rigard is a great healer to have on defense as one of the few cleansers. Should be on the left. Tiburtus is also good for the defense down, and better defense/survivability when compared to Grimm and Gormek. Obakan being fast makes him nice for the wings, but he’s still not an amazing defensive hero. He’s alright though.
K, so those are just my thoughts on all of your 4* and 5* defensively. Now, I’ll brainstorm a few setups for you. Up to you whether you wanna use my ideas, or build off of em. Again, feel free to ask any questions you may have over any of this.
I’m sticking to rainbow, because it’s the most effective and easiest to set up. Stacking colors on your defense team usually ends up helping the opponent more than helps you. Makes it easier to stack and take out more heroes with one color. War, it’s a little different. A widely used strategy is all mono-colored tanks in your alliance, with strong vs the stack flanking/wings (purple & yellow are the best at that). So after knowing what color you’re doing, or if you’re just doing your best defense setup, will help me better to help you.
Fast or very fast in the wings (usually squishy, so they’re protected, and have enough to charge at fast), wreak havoc/important heroes (usually average mana) in flank to ensure they go off (and preferrably have a decent defense stat), and for tank: tanky heroes in both health and defense, that either hit the enemy fast and hard, slow the enemy down, or help their flanks do the same. Al moves from left to right, so keep all dispels, cleanses, attack buffs and defense downs on the left
Defense Team with What You’ve Got Leveled:
Caedmon-Kiril-Li Xiu-Cyprian-Scarlett
Eventual defense team with 4*:
Sonya-Tiburtus-Kashhrek-Li Xiu-Scarlett
Eventual defense team with some 5*:
Caedmon-Obakan-Richard-Azlar-Musashi
Could switch Richard and Azlar around if you want a better shot at Azlar going off more often. He’s squishier than Richard, but packs a hell of a punch if he fires.
Hope this helps. Idk if I answered your questions or not, so if you’re still confused/curious, feel free to ask
