Void is much worse than ahrims.
Runescape combat works with dice rolls. If your attacker rolls higher than the defensive roll of the attacked, he hits. Otherwise, he misses.
Max attack roll (MAR):
Max defense roll (MDR):
These are then multiplied by 10 and floored.
The style variable can be filled with 3 for accurate or defensive styles, or 1 for controlled styles.
The void variable can be filled with 1.1 for melee and range and 1.3 for magic.
The prayer variable can be filled with the bonus listed in-game.
The turmoil variable can be filled with the total bonus (as listed in-game) minus 1.15.
Example: If the bonus is listed as 1.35 in-game, the prayer variable would be equal to 1.15 and the turmoil variable would be 20.
Paleas also found that max attack roll can be multiplied by the following, when applicable:
Melee:
Abyssal whip: multiply by 1.1
Abyssal vine whip: multiply by 1.25
Barrelchest anchor: multiply by 2
Brackish blade: multiply by 2
Dragon dagger: multiply by 1.1
Dragon longsword: multiply by 1.1
Dragon slayer gloves: multiply by 1.1
(Full) slayer helmet, Black mask: multiply by 7/6
Salve amulet: multiply by 7/6
Salve amulet (e): multiply by 1.2
Ranged:
Full slayer helmet, Focus sight: multiply by 7/6
Magic longbow: always 100% accuracy
Magic shortbow: multiply by 1.1
Sharpshooter aura: multiply by 1.03
Greater sharpshooter aura: multiply by 1.05
Magic:
Full slayer helmet, Hexcrest: multiply by 7/6
Runic accuracy aura: multiply by 1.03
Greater runic accuracy aura: multiply by 1.05
You can easily calculate that Void is worse than virtus unless you'd have like 200 magic attack (in void)
That said, void can still be decent (ranged defence, prayer bonus etc).