[BitD] Is there a reason not to make a group roll all the time?
So I'm the GM of a long running BitD game. My players are a max rep Tier 4 assassin group. Most of my players have 2-3 dots in Prowl and Skirmish. One of my players have a Vet abiliy to make them take a max of 1 stress for both group Prowl and group Skirmish checks. And they also have a veteran crew ability so if they roll multiple 6's in a group check, it stacks.
My problem is I'm trying my best to challenge the players but I'm struggling. I can add dozens of extra guards, or clockwork automaton guards. I've added enemies with powerful magic artifacts. But at the end of the day, most of their heists come down to making group prowl checks to get past as much security as they can. Making group skirmish checks to demolish their target and any guards. If needed they can also call on their cohorts to also add an extra 4 dice on top of their own.
And because they're rolling like a minimum of 10 dice for any group check, there's very few times they don't roll a 6.
Unlike other systems like DnD or Pathfinder, I can't just raise the DC because they're up against more powerful enemies. I can increase risk or lower effectiveness, but because they have fine weaponry and fine tools they usually get a min of Standard effect. And they can trade position for effect if needed be as well.
My players still do individual action rolls at times, but most of their major challenges can be solved with group action rolls.
Have you guys GM'ed for a higher tier groups like this? Is this normal for high tier play? How would you challenge a crew like this?