My point isn't so much that the balance will be off initially, it is that setting a Tactical Marine to 13 means the low end of points gets cluttered a LOT and granularity is missing. It's a lost opportunity to reset the low end point cost (mainly of infantry) to something higher that will make it far easier to actually address point imbalances later.
Bog standard Ork Boyz are currently 6 points each. If it turns out they need help, would you drop them to 5? That's a sixth off their cost, that'll likely imbalance them the other way.
Gretchin at 3 points each... Can't really go up to 4 as a nerf (+33%) or down to 2 (-50%) to help them, or you're likely to make any problem they have far worse in the other direction.
Up the costs by a factor 4 and your Tactical Marine will now be 52 points instead of 13, the Ork Boy will cost 24 and the Gretchin 12. Suddenly, there's some breathing room in the system to make adjustments WITHOUT making things worse.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.