A documented Defender of the Crown no loss run. (Goal: level 30)

[Fatt_Shade]

Posting that starting save would be nice
As for your suggestion that pet dragon get 2nd lvl of chest on 21 is wrong. Some of his skills have limitations (mystic egg can get 70% hero leadership after 15th lvl pet, or pet wall can get 600hp upgrade only after 10th lvl pet), for number of chests/or rage cost reduction there is no limitations for pet lvl at all.

digger {
hinthead=pet_digger_name
class=scripted
script_calccells=calccells_digger
script_attack=pet_digger
attack_cursor=magicstick
place=2
level=2
default=level1
upgrade {
level1=level:0/green:1,red:0,rage:4,rest:1,exp:5,level:1
level2=level:1/green:2,red:0,rage:+2,exp:+3,level:2
level3=level:2/green:2,red:1,rage:+3,exp:+4,level:3
level4=level:3/green:3,red:2,rage:+4,exp:+5,level:4
level5=level:4/green:4,red:2,rage:+3,exp:+8,level:5
rage1=level:>0,rs:0,rage:>9/rage:-5,rs:1
}

This is original game settings, i think for DotC and CotA they are same, only difference is maybe exp gain connected to strenght of enemy army and starting difficulty.