OK something definitely has to be done about certain traits. I just won a insane/insane no city challenge with a modified version of this build. No cities meant no road building abuse and (almost) no technology, and no horses(!), but that didn't hinder much.

I used lucky as the fourth racial attribute to boost the mauls which worked well. Towards the end my cave bears defaulted around 105 accuracy which got further increased with the swarming bonus. I consistently got 4-8 hits with them.

For the sov I went with just death magic and then Brilliant (for the exp and spell mastery), Wealthy (I was hoping to be able to buy some horses but it not possible to shop with no city), Sovereign Bond, and Tactician and Cautious (might be useful since the game is lost if the sov is defeated, but I never needed to use it). Cruel as the negative trait (No brainer in no city challenge).

I had to hold off engaging enemies for 5 turns to get to 50 mana to be able to consume my first shard, but it was all pretty easy from there on. I managed to research Mounted Warfare using Libaries, but it was not possible to get any horses. After that I grabbed Drills for the extra army slot which helped some but was not critical. I got a few more techs from trading, but none of them useful. I'm sure it can be done completely without researching anything and completely ignoring the libraries.

Chaosti: I don't agree with your suggestion that consume should be reduced to 30-40 mana, because it would make it quite boring as a trait. One idea could instead be to requre the shard to be in a city's borders to be consumed. This would reduce the consumption pace but still make it an interesting trait for an endplay where you harvest all your shards before the final battle (quest or conquest).

Beastmaster is overpowered the way it currently works. My suggestion here is to nerf it by only allowing taming of beasts which are same or lower level than the caster. It would still be an interesting pick but not allowing it te be abused like now. With a level limitation it could even be a little cheaper mana wise or with less cooldown, greater range or AoE.

The road building trait should be nerfed by (a) increasing labor cost, ( consume a step or end the turn when used, and (c) be available to all races.

Cull the Weak should be changed so as to only be allowed to be cast on trained units; I agree with that.