Instead of giving Alpha Shield complete invincibility to damage, give it an extremely high strength and if it breaks while active the ship also dies. This gives it a glaring flaw like any alpha version of technology would have.
Shield strength wouldn't change between levels, and upgrading the module would increase its duration the way it does currently. However, upgrading Alpha Shield for longer duration would mean longer opportunity for it to take max damage and get destroyed. A visual touch could be that it turns closer to red the closer it gets to imploding.
Early players using Alpha Shield shouldn't notice any gameplay difference as "extremely high" will mean the same as "invincible" if it never gets reached. It's effects will essentially be the same and upgrading it provides the same benefits (protects more damage per second). This would be true in all star types.
This change would be more reflected in high level gameplay where Alpha Shield + vengeance is a risk-free combo in all star types. If players can burst an Alpha Shield before vengeance goes off, it gives them a way to defend in BLS and WS and gives the attacker a bit more risk to consider when using that build.
Relates to this thread without a complete rework, where I first commented this idea: https://discord.com/channels/255083954036670464/1327172911315812382