It'd sorta be RPS kinda. Veigar would 1 shot Nasus (the ult would do over 12k in that vid). Nasus has no health bonuses. Drop a stun, ult him. As long as you kept him out of range, you win.
BUT, Sion would have much more than that, so he could kill veigar because the rest of his spells don't scale enough to burst ludicrous health down. Nasus might though. If he has Kitae's x6(assuming it's ARAM map) that's 15% of target's max health per hit and +240% attack speed. Couple in siphoning strike and you should win.
Thresh... meh... the rest have way too much burst but if thresh hits a hook and a flay, he might get veigar or nasus down but not gonna get Sion.