Funnily enough, though this would help Completion Ritual, it would have a harmful effect on the titan keyword. Right now, when you proc the keyword, you have an equal chance of getting any of the titan cards. With your proposed change, it would be more likely that you would get a common.
Old version: 1/3 chance of drawing a common, 1/2 chance of drawing an uncommon, 1/6 chance of drawing a rare
New version: 130/1500 + 1370/4500 =~ 39% chance to draw a common, 87/1500 + 1370/3000 =~ 46% chance to draw an uncommon, 2/500 + 1370/9000 =~ 15% chance to draw a rare.
This assumes you have all titan cards in your deck (a pretty reasonable assumption for someone going for titan victory), and none of them in your hand. The cards you have in your hand complicate the calculation, but it doesn't change the overall effect of making it more likely to draw a common and less likely to draw an uncommon or rare.
(I must have been really bored to want to do these calculations.)