At high level XP play the system has issues with Damage/soak balance and Success/Failure balance.
If despair/triumph cancel each other that should balance out Somewhat.
One of the main issues with combat success/failure is that not everyone has access to the defensive talents. Another issue is that the use of the defensive talents is costly in strain. The first issue can be handled by allowing people to have access to a number of levels of defensive skills from a base pool open to everyone. It's very hard to create a character that is defensively unbalanced, so this won't likely be an issue. You can however restrict the total number of levels you can reach. Giving access to the defensive skills can solve one part the success/failure balance issue. The next is the insane strain you'd have to pay to use a high level of defensive talents. It's easy to simply pay only half the strain.
It takes 10 upgrades getting from 2 purple dice to 6 red dice. 6 red dice vs 6 yellow dice has a propability around 50% for success, so the dice themselves are very well balanced. This makes it a lot easier to work with and balance the system, than for instance WFRP3.
So if you had 5 levels of melee defense, 5 levels of ranged defense and 5 levels of dodge, then you'd be able to upgrade attacks by 10 levels. It would cost 10 strain for one attack and of course dodge being more expensive as it only works for a single attack.
So it's not hard to balance this out, it's just that getting many levels of defensive skills is hard. If everyone has access to 2 levels of each from a base pool and you could never upgrade the difficulty by more than 10 levels, then it could work out. If for instance you have bought 2 levels of dodge from the base pool and then advance in a tree that has dodge, you have the option of ticking the dodge in the tree for free (without getting an extra level) or purchase it and get an extra level.
Perhaps adding two or more levels of soak to the base pool of talents would be alright too.
Then it's just a matter of setting the price for these base talents. You also have to take into account the price of the base skill versus the individual prices of the talents in various trees.
There is more to game balance than characters. You need to look at what you provide in the way of environmental factors. Cover, concealement. alternative methods of winning encounters. throwing non combat encounters. etc. I have not seen the balance issue discussed here in the high level play I have played. But then my GM throws varied encounters and makes a point to make thinking your way out of encounters including the combat ones important.