I had a Decker fire a rocket last session, if he fires a few of those he'd likely completely butcher any enemy he fights. It costs a lot of cash, but he can butcher tough enemies with it.
The same applies for Downtime Summoning and Binding. As long as you don't allow "resummoning until you score enough services", which Top Dog made a topic about a while ago after we considered it iffy, it's not that unbalanced. Those services are costly, even with the use of Edge. You're generally looking at an edged 400 per service on a Force 6, which means that this fight cost as much as an anti-vehicle rocket for the two mages, and that's excluding any other services they may have used before. And if the Spirits happened to get disrupted, they wouldn't be able to call on them for 3 weeks.
As for the Force 8: Do they have Magic 8? If not, there's the potential houserule in my list about them, which was a core rule in SR4 Street Magic. Makes them much harder.
Anyway, Binding costs points and nuyen. And something that costs a significant amount of resources tends to have a big impact. Rockets, expensive gas grenades, a bound army, they all cost effort and resources and when a player pulls out the big guns, it will quickly wallop many enemies. I don't think this is too big of a problem, as long as the summoning+binding rolls are made fairly, since it's what a Mage is all about. A conjurer can pull out a defensive army if they need to, but it likely costs them the same as a month of Low Lifestyle.
If you still want to heavily balance it out, the easiest solution is for everyone to agree to follow Missions rules and buy hits for the Summoning+Binding combo. With 16 versus 6/12 dice that's 3 services for 3k nuyen, so 1 for 1k. That way the players don't get to Edge for lots of services, plus they don't score as big an advantage, so the bound services are far more expensive.