I used to play this deck (or a tweaked version with around 40 cards, which seemed to me to have a better balance of aether pillars/PUs/Pegasi) a while back. I actually used Dim Shields in it in the end, and played it against False Gods...I believe my record with it was 52 games, of which I won 11, 10 against Miracle (with a 100% record, I was extremely fortunate he kept popping up) and one against rainbow, who failed to draw an electrum hourglass and was consequently slain by an INSANELY lucky draw.
I prefer to play 6 Peg/6 Bless/1 archangel/1 morning glory/1 miracle when I play my old deck in PvP now, simply because the faster damage from TU is, in my opinion, offset by it being approx twice as slow to play (going off the incredibly unmathematical technique of two elements = half the pillars available). I like Mirror Shield because it's INCREDIBLY cheap and can pose real problems for some decks that would really like to finish you off fast, but can rarely find room in a peg deck.
As the comments suggest, it's fast damage that can be made to look very foolish indeed by hard counters that are played early - when played late your hand tends to have built up a nice collection of fast damage cards, which if you have been wise with your quanta can be rapidly deployed for what SHOULD be an instant kill.
Some cards that utterly destroy this deck if gotten out on time:
Devourer (bye-bye air quanta)
Lobotomizer/Mind Flayer
Eternity/Reverse Time
Dim Shield/Bone Wall.
It shouldn't struggle with Diss Field - the few times I've seen players attempt this shield against a dive deck it has fallen and taken all their precious quanta with it.
As a final note, I wouldn't upgrade Pegasi.
Pegasi are a 3/2 with dive. With Blessing they can become a 6/5 with dive, essentially 12/5 assuming you have the quanta.
5 hp is the sweet spot in between Elite otyughs and Grav Shields, and utterly rips apart gravity decks which are simply not designed to cope with damage this fast (essentially, for 6 light quanta you get a 12/5 creature by around turn 2. Further Pegasi are admittedly limited to 6/5). There are ways around this for grav decks (most obviously, momentum), but I think the chance to hit this sweet spot outweighs the negatives, especially given the opportunity to build up and rush. Elite Pegasi are a 3/4 with dive. Against grav decks they have a choice between becoming oty fuel or viable damage, not both - making your primary source of damage your weapon.
8 damage per turn is nice, but not brilliant.
