No as the two don't increase on the same scale; if both increased on a 1:1 scale, your point would be stronger but since your damage output will always be higher than your ability to reduce damage, it becomes less of a potential problem as you pointed out. You're also not factoring builds that do not need to utilize the damaging output of those stats but the actual durability of them to be a build, such as bios like Ronin who gain spiritual durability and Spiritual Ken or bios like Rock Lee where they have no use for the damage output of a Spirit Attribute but can make use of the defense given.If you get damage shaving as an auto bonus of increasing your damage, both things just cancel out... Wouldn't it be better to keep them separate? You need to invest points in both damage boosting and damage shaving. If by every point we spend I we get +10 damage boost and -5 damage shaving, overall we just increase the damage by +5 points, no?
The purpose is to make sure every stat outside of Vitality is needed and useful outside of just damage as all bios will not need to invest in some attributes for damage but for other reasons.