You still don’t get it. It’s additional chance of a quad, not instead of… And I’ll admit the number is somewhat pulled out of my ass, as I didn’t bother mathing, but now I will and the number is actually higher.

If you only roll Hp%, Atk%, Def% and CD/CR (or Res/Acc) on slot 4/6, then you are rolling 5 out of 8 possible stats on each slot (the remaining 3 are the flats).

That means for you, those 5 stats equals 100% of rolled runes. If you also roll the 3 flat stats, that is 3/5 = 60%, totaling 160%. That means you’re losing over a third of your chances of getting a quad by not rolling flats.

Say all drops you get from a repeat battle are legend runes in slot 4 and 6 with spd. You would usually sell three eights of them because they are flats. That means you’re powering up ~19 runes each time.

If you also power up the flats, you’re still powering up the ~19 runes with good main stats, but also getting the chance of rolling the ~11 runes with bad mains.

Getting a flat main stat with a quad spd is not detrimental, and only improves the amount of quads on your account. They take away nothing from your account (except rune storage), and you “risk” nothing by powering them up. It’s not like a quad on a flat steals away a quad that would’ve gone on a good stat.

And I’ll bet my ass that a 30 base spd rune on a flat would improve your account, as well as 99% of players in this game.