Much better if there a 4 and 5 star version of swift buckler that give a PIERCING def and NORMAL def + 5 star version will have VH Asi
4 and 5 Star Version of Swift Buckler
the speed combined with the normal defence would already be too OP, but why piercing defence too? why not just have blitz needles that you can run around with while shooting and sudaruskas as fast as strikers?
the Strike Swift Buckler its a Boost shield, not a defensive shield prolly will work good on Tier 1 and decent on Tier2, but for defensive purposes in Tier 3 NO. even if they add a 4 and 5 stars version of this shield i think they will decrease the ASI bonus since this shield sacrifices the defense for a Boost in the speed so i guess if someday OOO add a 4 and 5 stars the shield will have a drecrease on it asi (prolly med on 4 stars and low on 5 stars).
But anyway this shield dont need a boost in it defense its OK as how its right now. maybe you need to work in your skills if you going to use this Shield.
So -1 to your idea.
What you can do is a reversed upgrade. 4 and 5* get more defense, but ASI bonus lowers instead.
Er....I think that's overpowered..