I'm no good at writing lengthy arguments so I'll go with these points:
30 seconds as opposed to 45 seconds (optional but usually always chosen by many in D1)
Can be broken by conventional weapon fire
Only supplies armor of light, blessing and weapons of light have been removed
Cannot generate more orbs as it is continually damaged
Death usually accompanies a nova bomb that was thrown from outside onto the shield, which makes no sense
The only thing that was improved is the deployment time and animation, everything else was shit on for some reason.
And yes I know that we 'have two supers in one', but defender has been gutted. At least make it so it can't be destroyed by gunfire.
Sentinel is also way more useful in blocking damage as you can actually move around while doing so, but sometimes you gotta protect a zone or your allies, rather than just yourself.
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Purely due to the way D2 functions now design wise, and the fact that the Defender class as a whole was reworked to become the Sentinel we have now. WoD cant have so many options now that it's only a single perk on a skill column, as opposed to the focal point of the class.