UR doesn't mill as well as esper does. Nehalia Drownyard with things like thought scour etc are probably better. Esper gives you access to the sweepers like Terminus and Supreme verdict and control cards like azorious charm and sphinx's rev.
If you're intent on doing mill then I think you need to try to work towards the Esper list.
if you're intent on staying UR, then UR delver is still a thing. Though the deck runs snap casters and a lot of counters and burn.
For UR delver, you'd want 4 delvers, 4 snaps, and maybe a couple Ætherlings as creatures. You need think twice for your draw engine and Ral Zareck wouldn't be bad either.
Pillar is a solid card and I wouldn't worry about changing it for now. Who knows what will be available after rotation. When rotation happens you'll have M14 and Theros cards to consider. They could bring back lightning bolt for all we know.
Other cards to consider adding.
Mizzium Mortars - strong damage for cheap cost, efficient sweeper
cyclonic rift - more of this
Burn - remove creatures, searing spear, pillar.
More Duel-type-lands and land in general - a control deck needs to be at about 24-26 lands to be consistent, even with additional draw cards.
Turn//Burn - great removal for tough to deal with creatures
Think Twice
Counter spells (dissipate, rewind, syncopate) - these spells exile cards which is a really beneficial effect
Auger of bolas if you can't get snap casters
if you wanted more reslient creatures you could even try Reckoner instead of delver.
Ætherling - Ætherling - Ætherling!!
Cards to consider taking out
Spell rupture - weapon surge (you're not running enough creatures to make these worth while)
Clear a path - I've never seen enough defenders at FNM for this card to matter.
All the mill... - to be honest it's not an efficient strategy and it can even help some decks right now.