Why do you think it's only viable to put combat ability points in Polymorph?
With a point in Necromancer you get for example more self-heal through damage. A point in Warfare ups the damage against physical armor by 10% which may be better in some occasions than a general increase of damage by 5%. A point in two-handed gives you 5% damage and some crit chance.
A point in Polymorph gives you an additional attribute point. Which is nice of course. But with the second benefit of attributes (for example + physical armor for Strength) removed now, you get not more or the same than from a point in combat abilities, but less. It may be a good decision to put points in Polymorph for an Intelligence based build.
Then there is the rumor that higher skills need several points in the according combat ability. Which is in my opinion absolutely necessary for the health of the game, as it's biggest fault is the easy way to amass ubar skills from several schools.
No one said it wasn't viable, that's a strawman, nobody said that. Additionally cherry picking situations is also another flawed argument, as it doesn't represent overall balance, so let's move on from that point as well.
There's a difference between viable and effective.
There needs to be multiple "effective" roles because that's what a well designed game consists of, not a end all be all min/max single option.
It needs revision.
Before you asked why I haven't addressed the rest of your post is because your post relies on a flawed premise. Therefore it is pointless to argue the remaining information you've provided as the premise it uses as its foundations is logically flawed.
Additionally, if you have any official word of balance changes going into the game at launch that contains changes that would alter the balance of stats, please provide them. Otherwise I'm going to assume based on no other current knowledge, that what we have now will be similar if not identical to what goes in at launch.