Confused about heavy vs normal stun and building around it. (Wall of text warning)

As ive been playing the game ive found that killing enemies through stun felt fantastic especially with boneshatter to clear packs quickly.

The problem arises when trying to build around the stun mechanic as much as possible. A lot of the payoff in damage is through "heavy stun". The game seems to describe two different buildups, stun and heavy stun buildup, however I'm pretty sure there is no such thing as heavy stun buildup as heavy stun is only applied by certain skills when an enemy is "primed for stun" through normal stun buildup.

It becomes more and more difficult to heavy stun normal enemies and clear them with boneshatter as building more stun buildup causes you to end up stunning them in one hit, which is not a heavy stun because they must first be "primed for stun" to be heavy stunned. This means I have to do this janky thing where I have a low stun buildup skill with high attack speed to prime normals reliably and a bigger more damaging stun skill for rares and bosses.

This might seem interesting at first but what happens sometimes is I have to respec my skill tree and swap support gems around to have less or more stun buildup since the stun I need for my skills is always changing as I progress. This makes it feel so awkward to play since I made the mistake of relying on this mechanic.

Sorry for the wall of text, is anyone else having the same issue? I wish there was a support gem that could allow a skill to build stun but not actually stun, leaving the bar at 99%.