Talent upgrading abilities seem to follow a trend - they make it 50% stronger. Examples would be upgrades to Arcane Veil, Lay on Hands or Flames of Devotion.
How does Critical Focus compare to them? Very poorly, unfortunately.
Zealous Focus gives 6 accuracy (let's ignore second bonus for a moment). To make it 50% more we need 3 more accuracy points. How much is 3 accuracy? In best case it converts 3/100 from misses to criticals:
3 * ( 1.5 - 0 ) = 4.5 weapon damage / 100 attacks.
Not bad. But there are situations where accuracy gives less. It may also convert misses to hits or grazes to criticals. How much weapon damage per 100 attacks is that? Let's see:
3 * ( 1 - 0 ) = 3 weapon damage / 100 attacks.
3 * ( 1.5 - 0.5 ) = 3 weapon damage / 100 attacks.
And now the Critical Focus, that converts hits to crits. Max hit chance is 50% so it can affect up to 2.5% of your attacks.
2.5 * ( 1.5 - 1 ) = 1.25 weapon damage / 100 attacks.
Ugh.. that's bad. It's 3.6 to 2.4 times worse than it should.
Fortunately Obsidian is not afraid to do 'doubling and halving' even after game release. Heck, they even divided some skills/spells by 4 or 5! It shouldn't be any problem for them to triple Critical Focus bonus.