@nungnum In theory, if you are playing a deck like this, you would want to go for the I-win stuff. Our tip off for that being the way to go is that we will have to populate our deck with "weaker power level" cards.
Now as you may or may not know, one of the best ways to start arguments around here is to start calling cards "lower power level" and stuff like that. Very soon you find yourself out by the swingsets, arguing about whether your dad's Balance could beat up some other guy's dad's Timetwister. It's just not were you want to be. But with that said, I will at least posit that this deck will carry some lower power level cards.
What I mean by that is for us to look at how much and how often a certain card improves our chances to win when we see it. Arguing aside, that's the basic equation for card "power": (Average improvement to winning chances) x (Likelyhood that we see the card) = card power... basically.
First imagine the best (most broken) theoretical card. Imagine a card that just says, "show this card to your opponent at any time: you win the game." That card would improve your winning chances a ton. 100% subtract whatever your chances to win were in the first place. Imagine if that card had another line of text on it that said, "If this card would begin a game in your sideboard, you may put it in your hand." Now that gets us to "seeing" it 100% of games. 100% chance to win x 100% of the time = 1000% dumb. That's what maximum brokenness/power would look like in theory.
So what about Black Lotus and Moxen and Ancestral? They almost always increase your chance to win, and they do it, on average, by a lot. The cumulative effect of running those power cards is big. Now, with Flash Rector, sure those are powerful cards, don't get me wrong. But this ain't modern we're playing here. By playing Rector, you are not playing some other powerful cards. Bazaar, Oath, Paradoxical, Workshop. Those cards improve winning chances substantially and consistently. Rector probably doesn't improve winning chances as often as those other cards when you see it in hand or play it.... but.
It can improve winning chances MORE. If you play Rector, or Flash Rector, you are going to want it to go off big time when it works. You are going to get futzy hands with three Rectors that don't do anything. (Trust me, I play Oath. It sucks.) So when you get the god-hand, you better make sure that you design the deck to make you the god of actually winning. Rector Flash turn oneing an Energy Flux into play is... well it's just not that broken, and I mean that statistically. You just flash-rectored on turn 1 and the other guy is still alive? That's just wrong. The thing that made the Protean Hulk build bad, was that it played Protean Hulk and a ton of weird crap, that did nothing and lost terribly in any sort of control war. If anyone ever got ahead in counterspells that thing folded... well, like a deck of cards. But the thing that made it great was that when it hit, as you pointed out, it killed you stone dead.
Decks with "weaker power" cards in them can be great, when they combine to exploit synergies that actually demonstrate that those cards aren't as weak as they seem. If they cause winning, they are powerful. That implies that a combo deck like this should contain combos that win the game as surely as possible when they go off.