His deck is really good but I believe cutting one iron core and replacing it with a 3rd urnight is actually better, since he runs 3 diamond cores the chance of not having the iron core in hand after gambling is very low, also he usually needs ice or sandman with one Maximus on the field and I don't believe he ran into any situation where he needed 3 maximus on the field.
All I'm saying is the diamond core is counted as 3 iron cores or 3 urnights so the chance of bricking is very very low after SUCCESSFUL GAMBLING but opening with urnight or having 2 urnight in hand is actually better than having the iron core cuz sometimes the iron core is a dead card.
3 maximus just to draw them early, Maximus is not a dead card, the diamond core can easily search for the iron cores so most of the time you will use both of your iron cores, 2 cores for better staring hand without hurting the consistency, this only works with last gamble and draw sense wind tho, with balance you need 3 iron cores.
I hope you understand what I'm trying to say.
I have been playing this deck for too long, even before we had the diamond core I used summon Maximus once or twice in one duel and the 3rd usually get discarded as a cost, with the diamond core now it's just like you have 6 iron cores.
Having 2 iron cores in your opening hand is usually not good especially if you didn't draw urnight or the diamond core but drawing one urnight and 1 core is great.
Look at Balance deck, the 2nd one, he knows that he may draw only one spell in his starting hand and he wants it to be the core (iron/diamond) so 3 iron cores are mandatory, he also knows he may draw 1 or 2 monsters that's why he only plays with 2 Maximuses to reduce the risk of drawing 2 in his starting hand, 3 urnights in his build are extremely important.
A Very good build!
I'm kinda tempted to build one that also include Koa'ki Meiru's anti LIGHT/DARK cards due to how prevalent those two attributes are in the current meta.