[Executor]

I'm sorry, but I find playing SP Dominions like this completely idiotic, the PD way I mean.
There are infinite ways to kill the AI, and if you can't beat the AI than it's still not time to try MP.
You can play the same way the AI plays and still beat him easily, just field your nations best troops, no mages no spells, no nothing. Take a nation like Midgard for example and only make skinshifters. Or Agartha and just make Troglodites.
AI tends to use crap troops like militia and other crap which break and rout easily.

Second way to play is just research battle spells. I think that's self explanatory, as the AI has hard time dealing even with the most pathetic mages.

You can just summons a few medicare thugs like Bane Lords and semi-thug them out. Than there's the choosing of any bless nation with a decent bless.
AI can't deal with Kailasa due to awe, can't deal with Micltan, any bless nation really.
You can also take a Giants nation, Hinnom for example, Niefelheim and *just recruit commanders. Take crappy scales and some OP bless and make just a thug Giant commander (Jarl, Melqart...) and send them out one by one. Equipment or buffs are optional.
Than there's death magic, AI can't kill any death nation with raise dead/skeletons.
There's always the take SC awake pretender (Dragon works best) and kill the AI on turn 5, than move one to the next one and so on.
Doing some minor site searching than spamming a ton of summons (note than the AI doesn't site search and therefor rarely uses summons)

Now, you can't do that with human opponents cause nobody really uses PD, unless you expect a fight in your province at which point you probably up the PD to 25 at best so the PD fights along side your troops.
The reason nobody buys PD, or buys very little until much later in the game, or not at all more commonly is that PD is useless.
The money spent on PD is better spent on troops/mages/forts which will be used to take more provinces faster, which will bring you more gold, which will bring you more troops/mages/fors and so on.
PD gets taken out quite easily with minimal or very often no loses due to lack of battlefield orders. PD Archers for example can get screwed by only a hand full of troops placed correctly, and all the other gets screwed by battlefield magic since they're all grouped together or enemy archers.
Or you can just send a thug with say luck and body ethereal and rape any amount of PD.