I like this!

I like the design, but it's more like a black boardwipe than a white one.

I don't think so. See Divine Reckoning and Tragic Arrogance.

This is not meant to be a balance effect. It's a board wipe, but if you have the angel, you get to keep a guy.

Oh, right, it turns into Duneblast. Duneblast is an absolute blowout, close to an instant-win button, but yes, I guess 6 mana plus an Angel requirement is probably okay.

The problem is that's exactly the difference between white and black's boardwipes. White's clear the board straight out, you can get advantage out of them but only in weird ways like indestructible that are attached to the card you're getting the advantage out of, not the boardwipe. Black's sweepers are built to create advantage. With those examples EACH player gets to keep a creature.

It would be too wordy to make the creature indestructible instead of just not destroying it. With the angel clause, I don't see there being a reason this can't be white. I could see it as black too at a higher cost, but it works mechanically as white.

White gets Martial Coup, Kirtar's Wrath, Phyrexian Rebirth and probably something else I can't give you of the top of my head.

This serves the same purpose: Level the field, but for an additional investment get a small head start. I like this since it requires more than just more mana.