Thank you, I had to create a cube on cubecobra and hence it took a few days. I put the cube in my signature, but here is a link
https://cubecobra.com/cube/overview/16se
Regarding the perceived OP cards:
Tolarian academy and
Serra's Sanctum suffer from the lack of having many cheap artifacts/enchantments. This makes these cards often quite a risk since they are a dead land drop often.
Gaea's Cradle is strong since every deck plays creatures and there are some cheap ones. This is definitely a strong card (
Deranged Hermit anyone?)
Metalworker is strong, but again, it is rare to have more than 8 artifacts in your deck.
Memory Jar reads as draw 7, play a land and 2 cards from those seven, discard the rest. So effectively a slightly better
harmonize.
Grim monolith is strong, it helps cheat out
Phyrexian colossus. Effectively the monolith is a slightly stronger
Dark ritual which was not strong enough in an early iteration.
Replenish is nice, but you are lucky if you have 8 enchantments in your deck. That said, returning a
Pestilence or a
Serra's Embrace is quite painful for the opponent.
Time spiral is potentially a dangerous card, especially with
Gaea's Cradle or other free cards like
Treachery. Still, it costs 6 mana and since there are no cheap mana artifacts/rituals it is a strong, but fair card.
To summarize: If you do not have access to 4 cards of each, most broken cards
falter. Urza block lacks cheap mana artifacts and has no storm payoffs.
There are some cards which will make the opponent groan when you play them.
It is possible and often happens that the opponent (barely) wins against these cards.