Just to compare...
Time Bomb v Unstable Gas
Unstable Gas
Playing Cost [6

] + Ignite (Duo Cost) [2

] + 1 Card + 1 Turn for 20 damage
Time Bomb
Playing Cost [1

] + Tick (Mono Cost) (x3) [3

] + 1 Card + 3 Turn for 10 damage
I'm disregarding UG's mass AoE in cost since it also affects both players' side, although without it, it'd probably cost more.
Time Terror v Lightning Storm v Firestorm
Time Terror
Playing Cost [2

] + Tick (Mono Cost) (x3) [3

] + 1 Card Cost + 3 Turn Cost for 4 AoE
Lightning Storm
Playing Cost (x2) [4

] + 2 Card Cost for 4 AoE
Firestorm
Playing Cost [5

] + 1 Card Cost for 3 AoE
Verdict:
Unupgraded is slightly OP in the face of UG, especially since it can targeted by Fractal or Mitosis, which is something of note with SoR.
Upgraded is definitely UP in the face of straightforward AoE CC. Could probably be compared closer to Improved Plague...