Notes & Combos
Seee notes from my S9 D1 deck, I had Crow and Belle in response to Branded's dominance. The Mathmech engine loses to Branded In Red resolving and these were the best answers.
However, this run faced much more Floowandereeze, Dragon Link, and Live Twin than Branded decks. Floowandereeze was the hardest matchup since Belle and Crow were blanks. Imperm is a lot worse with the new Floowandereeze quickplay spell so going 2nd to this deck was almost unwinnable. With this in mind, cutting DD Crow to reduce the deck size count, adding Psy-Frame Gamma and/or Droll & Lock Bird are options. Belle still has useful upside such as negating Called By The Grave which might be enough to keep it in.
Iblee and Parallel eXceed are the most useful Small World bridges. Iblee's strengths against Branded aren't too valued since you could run into Floowandereeze and this deck does not have Salamangreat Sanctuary to prevent Iblee from crashing.
Heatsoul is something to think about when you open weak, there are 2 flex spots with 3rd Alembertian + Link Spider for Heatsoul + Almiraj.

wouldn't jammer be better over a third alembertian? i don't see a third one coming in handy as a simpler way to otk but idk much about mathmechs (despite having it built) so I may be wrong.

Yeah I don't see an issue. I ran 3rd Alembertian for grind games or this extremely specific scenario: If I had no play (Diameter + Addition + 3 non-engine) outside of Alembertian searching Superfactorial and passing. You would Superfactorial T2 for a second Alembertian, search Diameter. You had this weird dilemma T3 where you might be able to OTK but wanted a 3rd Alembertian to use with that Diameter.
But as you said, this is not going to come up as much as winning those games where you have 3 bodies for the Update Jammer Accesscode play. Even in the scenario I listed above, Heatsoul would be a lot better!