There is only one deck I think capable of running 70, the rest I stick to 64 or less. That deck is Guardians of Light. 6 draw creatures, 3 tutor creatures, 4 insanely good tutors. Imo, it runs BETTER at 70.
But if you go to 70 there are now 10 extra cards between you and the card draw. Even if you do get the draw, it now has to trigger an additional 10 times to get you to that card you need.
In fact, since you like using anecdotal evidence, allow me to attempt to use it against you here. I used to play Wizards' Star Wars TCG competitively back in the day, which was very similar to MTG in a lot of ways, including minimum deck size. For a while I got into the habit of building a 60 card deck and then throwing 1 extra card on top. Card draw was plentiful in that game -- really, really plentiful -- and like you I figured it would compensate for having an extra card.
Well, in one tournament I got through to the semi finals and lost the crucial game with that 61st card sitting quite uselessly in my hand. After the game ended I did my usual habit of checking my next 3 draws, and the very first one was a card that would have let me back into the game. If I'd been playing 60 cards I'd have drawn it and at the very least put up more of a fight, if not won. I nixed the 61-card habit then and there and have never looked back.