:eyebrow:
For serial?
Seismic Assault isn't removal, it's burn. Burn can be removal, but it's also a win condition that doesn't require the red zone. That means that it gives the deck reach ("You're at three life after my last attack. I could attack you again next turn, but that gives a full turn to interact with me and my board, so instead I'll just burn you out and win now.") and a way to win outside of the red zone if you can't get a guy to stick, for whatever reason.
EE is mass removal that can potentially hit multiple permanent types, making it much different in terms of function than green Vindicate. EE set to two can hit both Tarmogoyf and Counterbalance in one activation, and it can also wipe out untargetable creatures or potentially take huge chunks out of a Merfolk or Elf player's horde. Maelstrom Pulse doesn't do that.
Pulse is closest to Terminate because it's a narrow targeted removal spell designed to clear out annoying blockers or potentially harmful utility guys, and it should be under consideration for that slot. However, Pulse isn't clearly better because, while it has a lot of flexibility in terms of what it can hit, it's competing for a spot in an already crowded point on your curve, and it's only a sorcery, making it much easier to play around. Terminate's appeal is that it both smooths you curve and can be played in response to things.
It could also potentially have a spot in the Wish board, but I'm not sure what it would replace or what strategy it would answer.

