If that fish is in your DT tank it is bad news. It does not matter if its ich or velvet. You need to treat it in a QT tank somehow and let your DT tank go fallow for 76 days.
I think the answer to your question is... "yes". Velvet is certainly more deadly than ich. But even if that is ich, it is not just a spot here or there. I would assume velvet, because the treatment protocol is the same. Read up on ich/velvet treatment and fallow periods in the disease forum. Of course, if you become confident that it is only ich, and you can tolerate occasional outbreaks like this, you can opt for "ich management" where you try to lessen the severity of outbreaks. But there is no way to eliminate ich or velvet from your DT through "management".
The rule I have seen for identifying ich/velvet, if you can individually count the spots then it is ich. If it looks like a dusting on the fish that you cannot count with your naked eye then it is velvet. In this case you can see the individual spots so I would go with ich. Just because a fish has one does not mean they are void of the other. So it could be ich and velvet. Either way I treat all parasites, some prefer to just manage.