Firstly Tyrion. The guy is ridiculously OP. He is surrounded by allies and always snowballs into a mega empire by mid game especially if played by the player. With his bonuses you can easily do the campaign on Legendary without breaking a sweat. So firstly just take his upkeep reduction and replace it with nothing. This will balance his ability to churn out armies.
Secondly the High Elf roster is way to strong with to many units. Make the DLC units only available to the LLs they come with and this will balance the faction in campaign perfectly.
Next they need more enemies so move Tretch to the White Tower with a decent stack and this will be a lot more fun and challenging as it's just to easy. You can justify it by saying Tretch tricked Teclis which is why Teclis is banished.
Finally reduce Tyrion's melee attack and defence by 20 each as he just cuts through everything. This will make him a lot more balanced as he is barely being hit while killing all.
With Teclis remove his parrot mount. He never had it in the lore and it's ridiculously OP. Next half his WoM as he can easily kill 500 in a battle and it's just a lot. Teclis in lore is more behind the scenes.