Here’s what I was running to farm focus:
Saryn Prime:
Range is the absolute most important. I even notice a difference between 235% and 250%, which is why I have Cunning Drift installed (200%+ is all really good, though). Next I’d prioritize strength, as you really want to score kills with spores. After that, duration. Efficiency you can work around with Zenurik/orbs/pizzas.
Ignis:
Sinister Reach and Firestorm are the key ones. I don’t even really care about the damage (although Radiation or Corrosive melts Grineer at Helene up to wave 20, even with two non-damage mods), the Ignis is there to spray acid/radiation everywhere to pop spores. Firestorm will have it hit through walls easily, and sinister reach can hit most of the map from the defense objective.
I usually immediately drop a Molt and start placing spores on it and blow through Wave 1. It’ll pretty much be an instant-kill as soon as they spawn, but you want to clear the wave ASAP before picking up the Convergence orb. Wait to see if the lift is moving up or down and time your Convergence pickup accordingly. From there, it’s just kind of a mini-game of maximizing Convergence orb timers if you absolutely want to squeeze every drop of focus out of each wave. Pop your #4 on a molt full of spores in the last few seconds of your Convergence orb to knock out those lingering Nox and Eximus enemies, which have big focus payouts and often survive your spore plague.
If you’re grouped with another Saryn Prime or Banshee Prime, don’t worry too much about maximizing orbs, just make sure to have a weapon with a Lens equipped while you spam your spores. You’ll still get really good affinity/focus as long as you stay within affinity range of the other saryn/banshee.