To put things in perceptive,
1) In DD, the max skill level you can reach, without item bonuses, is 5.
2) In DD, there are items which gives bonuses to skills
3) In DD, there are skill-books which increases level of skills
If BD has those, then I think the lack of skill points isn't be too big. And, maybe there are
4) Quests which award free skill-points
and remembering that
5) Every 5th level gives you 2 skill points per character, which means 4 throughout.
But all that said, I agree - the shield skill tree is not a very good idea. Rather, the shield skill tree shall protects against the attack type instead of enhancing the attack type. This means you will lose all effectiveness with the weapon or you gain half, or even better, put that percentage as a skill. So the shield skill tree looks like this:
+ protection vs. piercing
+ protection vs. slashing
+ protection vs. crushing
+ protection vs. bone etc. etc. etc.
weapon skill percentage (maybe initial at 20%, +5% per level)
