Definitely lose a lot of damage when dropping serums, but can make up for it by increased AOE and snappier target pacing.
Playing from the tray, with a basic attack and then a full rotation from left to right, plus sig whenever it's off cooldown.
Need to place the shield toss at the start. Even though it won't benefit from the extra damage from when vulnerability gets applied (on the following attack), it helps pace the return of the shield in your hand so it won't stop you from using a later skill that requires you have the shield in hand to execute.
By switching off serums, meteor kick is rendered obsolete and loses it's bonus damage potential and execution damage, so need to drop it completely and keep both shield toss/bounce in the rotation.
Rotation ends with shield bounce banging off enemy skulls while you spam your basic attack to recover any lost spirit. Shield will return before cooldowns are ready to go in full if you aren't interrupted mid-combo.
Drawback of this setup is having to stand in one place to keep spamming abilities. You're much less mobile here so building up some defense helps, and keep spamming the medkit as you'll be eating damage while carrying out several attacks.
It's definitely a complicated playstyle, and you may need to button mash to ensure animation issues don't interrupt you from carrying out an attack when it's next in line. Can see my rotation failed a few times.
Overall gives Cap a bit more AOE and may be an easier playstyle for folks struggling to manage spirit/serum gen.