I agree with Vich about the status effect and seeing the mob hit you when using Aegis Boon, rather than trying to time phalanx when you see a +HP gain.

The stopping when running bug because of your shield dropping is very inconvenient. >.<

I like the current shield system. Deflection, Ageis Boon II ect... they are very helpful abilities that let gladiators regen precious stamina that is vital to effective shield/stamina management. The status effect that Vich mentioned would be very useful, but in my opinion this would take some of the fun out of gladiator and would eventually lean more toward changing the whole shield system and leaving GLA shields up at all times.