What would you suggest swapping for Sphinx of Magosi or Medomai the Ageless?

I'd remove Jace Beleren and Yosei, the Morning Star. I feel Jace Beleren gives to much card advantage to opponents, while you don't have enough ways to trigger Yosei, the Morning Star's ability.

I was actually thinking about Jace Beleren. Yosei is actually really useful at tapping down problem permanents and has proven plenty of use

I don't if I should swap Jace Beleren for Sphinx of Magosi. Jace is cheaper to play and has no activation cost, but isn't fetchable with Isperia the Inscrutable and provides advantage to everyone. Sphinx of Magosi is fetchable and only provides advantage to me, but is more expensive and I have to pay for each activation.

So, a few things for a competitive deck:

• Mana ramp. I get that U/W isn't super great but you have many artifacts available to you which will greatly help. Especially for such a hard costed general. Things like Chromatic Lantern, Marble Diamond, Sky Diamond, Burnished Hart all really help to get mana down quickly.

• Card draw is super important. Your general may be a toolbox general, however that doesn't mean you can skimp on the card draw. Especially when you need to deal combat damage to trigger the tutor. You're not a Captain Sisay or Arcum Dagsson deck, you can't just tap to do your thing. Especially when your deck is a control based general damage deck, you need access to removal and counterspells. I would recommend at least 10-15 seperate card draw/tutor effects seperate to your general's tutor. Good cards would be Enlightened Tutor, Mystical Tutor, Blue Sun's Zenith, Mulldrifter, Consecrated Sphinx etc. And look at the ones you already run - e.g. Trinket Mage fetches a whole 2 cards. Kinda crap. Now upgrade that to Fabricate and you can fetch everything. Yes, I know hes a creature which means you can recur him, all of once before he's a generic 2/2.

• Removal Base. You have a good chunk of counterspells and removal, however I feel like the cards you run could be tweaked a bit. Things like Logic Knot are not that great, as you pay a lot more than just mana. I would look into things like Swan Song, Mindbreak Trap, Memory Lapse and Lapse of Certainty - these two while not being hard counters are great for your general. For after- the-fact removal, Curse of the Swine, Path to Exile, Oblation are all really powerful cards.

• Utility. You have a toolbox general but you need to make her work for you. Cards like Gravitational Shift are great for getting through that extra damage. Capsize is an amazing card as you know what you bounce. Brago, King Eternal is awesome since he "untaps" your general and lets you trigger lots of ETB effects (since most of your creatures are ETB based). Archaeomancer lets you recur instants and sorceries. If you really feel like splashing out, Vendilion Clique is awesome for your general, ableit expensive. Since you don't have a huge amount of ramp available to you, Leyline of Anticipation is good in this kind of deck.

• Mana base. Why are you running cards like Ancient Den and Seat of the Synod? its not you run a Tezzeret the Seeker . you get no added value from them, but on down side a nice overleoaded Vandalblast (yes this happens quite a bit) will leave you two lands less. Seems not good. Also, EVERY competitive deck should run Strip Mine. No excusses. Its not about wrecking other's mana bases, its about dealing with that Gaea's Cradle that's tapping for 5 mana a turn. Academy Ruins is a solid recussion engine. And get at least a Flooded Strand, they're going quite cheap at the moment. A few fetches (you can run 7 total) + a Crucible of Worlds should be your end goal. It means that you will never get mana screw'd and you can very quickly strip your deck of lands.

I know this is a bit of a wall of text but hopefully it will give you and idea about more competitive deckbuilding descisions.