RSP I am not sure what you are going for here. You have been given the clear opinions of at least 3 different people that Dispel Magic targeted at the caster of Shadow Blade will dispel it. While I don't have time to look at all of them, I imagine any spell with a range of self will end up working the same way, they are dispellable if Dispel Magic targets the caster, likely all for the some reason. They are a buff/magical effect on the caster (this is what a range of self means), that can then be used to affect other things.

If you don't like that answer obviously you can rule/houserule differently in your games, or try to convince your DM too. But I am not sure how else to try and convince at least not without better understanding why you disagree with the reasoning so far.