I agree with most of your post.
The first 2/3 of your suggestions match 5e rules. In addition to being usable one- or two-handed, spears also have the Thrown property in 5e exactly as you suggest.
Pikes, again as you say, are indeed supposed to be two-handed weapons with longer (10 ft) reach.
As to the spear and shield skill, this doesn't match any 5e rules, but it does match well with the other 1x/short rest weapon skills Larian has implemented in BG3. I wouldn't be opposed to adding this skill for spear+shields (instead of the...charge, I think?), as long as it has the same limitation of 1x/short rest. If you want this to be usable at a higher frequency, then it should require a feat (Shield Master) or a class skill (Battlemaster Fighter's parry and riposte maneuvers).
