More useful to brick enemy guns and do battlefield control. Don't be in your secondary role when you could be in your primary.
I'm gonna go out on a limb and guess you've never played a Decker.
Anyone who has knows that hacking in Combat is an utter waste of time. First, enemies - just like Runners - rarely have their gear Wireless On. Even if they do, the Action Economy to do anything useful (prior to Kill Code) is too high. Kill Code introduced some new options, but since they are just as punishing against PCs, it is even more likely that no one will be Wireless On.
Not only is it simpler, for all involved, to never have anything Wireless On, it is also the best way to deal with the Matrix during combat.
the only winning move is not to play
I'm gonna go out on a limb and guess you forgot we're talking about Technos (which is my favorite thing to play, btw).
A Techno can just Puppeteer things into doing what they want with a single action. Plus, a TM with Overclocking can sometimes get that 4th pass in VR. If they're on Psyche, they'd get it almost half the time. More than half if they also went the cerebral booster route.
But extra, quicker options aside, you left out the part where I said
"unless you're caught in an ambush." Meaning, you should be able to hack all the things beforehand. And if that isn't the case, then yeah, action economy isn't on your side so much, even as a TM.
I'd rather not touch the wireless-on-or-not thing, because that's already been debated ad nauseam - repeatedly. Not much sense going through it all here, too.
But again, bricking and sabotaging guns isn't the only relevant hacking option. There's also battlefield control, since the lore says practically everything is wireless and hackable.
And if the enemy is anything other than gangers, then they probably have their own matrix specialist, so it's still useful to be online to deal with that. Even if they don't have one, drones are fairly cheap and common; there could very well be one or two of those you can use Confuse Pilot on (which doesn't even require any marks).
- Speaking of which, since the thread was specifically about TechnoRiggers, the Machinist Stream for sure allows Target Device as an option. Since everything in the 6th world is wireless-on by default, it's a pretty good bet that enemies will still be carrying
something that's wireless, which you can use to give your shooters bonus dice. (net hits -> bonus dice for every gun on your PAN to shoot at that device)