The problems are:

1) Even in those situations, does the societal value outweigh the harm to the employees who suffer under the weight of the non-compete?

2) Even if the answer to #1 is yes, is there a way to narrowly craft law that allows non-competes in that very narrow situation without the collateral damage of other employers foisting non-competes on employees in non-analogous situations?

On #2, my guess is the answer is no. We have bright-line rules for good reason - because without them, it is easy for an employer to get around them. They are a blunt instrument, but they work. A lot of labor laws are like this.

And remember, the situation you were concerned about - the small startup vs. big company situation where the startup cannot enforce its trade secret rights because of costs of enforcement - would end up being turned into an analogous situation in the employee vs. big employer context if we allowed more non-competes to be enforceable. Maybe the employee's legal position would be correct, but try going up against a big employer in a legal battle to fend off enforcement of such rights.

Maybe instead of playing around with rules around non-competes, we should be focusing on providing a greater ability for small companies to enforce IP laws? For example, better attorney-fee shifting provisions?

I think it's part of the ongoing David vs Goliath problem. My worry though is that it's last call for small companies being able to compete and grow.