2. Introduce a new shield-damaging missile which does not flak but also does more shield damage than the Sabot.
This used to be the case, and the Sabot was even stronger because it had better anti-armor and anti-hull. Single shot with more damage has better armor penetration. You cannot make sabots or its replacement do more shield damage without also making them do more armor or hull damage.
Sabot went through many changes.
First version was a single 750 damage slug. Slow enough that AI usually dropped shields to armor tank it. This made it only good either as anti-hull (where you want them to drop shields and eat 750 hull damage, and it was more reliable than harpoon) or to force AI to drop shields for another attack, like plasma cannon salvo. Of course, AI still used them as anti-shield, while player was better off using them as finishers like slower but more reliable Harpoons.
Second version was a wide shotgun spray. In theory, more damage to shield and less suitable for anti-armor/hull. In practice, AI always dropped shields and most of the burst missed because it was too wide, and what little that did hit the ship did negligible armor damage. Second version was totally useless aside from forcing the enemy to drop shields (so something like plasma Sunder can fire sabot, then blast with plasma cannon on unshielded ship - too much work for so little ammo)
Third version was back to first version, except speed was sped-up so fast that it was nearly unavoidable. It became the reliable anti-everything missile.
Fourth version is the current version. Not quite as devastating to armor as the third, but still powerful.
I would not want Sabots weakened without more ammo or less OP cost to compensate. I think Sabots are fine as a player weapon. AI is too stupid to use them to full effect.