Well DC already makes the Titans look incompetent so Vic taking down the Five by himself isn't gonna hurt what's already dead.
I look at it like this; there's no drama left in the Titans (as a team) fighting the Five. They've been doing that since they were kids and it's played out. We've watched the Titans grow, becoming more experienced and powerful, and while the Five have done the same in theory, we don't see it. So it ends up looking like a NBA team playing against their old high school rivals, but those rivals are still in high school and are not any better at the game than they used to be. It ends up looking like the Titans are either punching down, or haven't become any more effective than they were at 16, and it's underwhelming either way. If the Five had been shown to grow and improve as the Titans have, it'd be a different story but for the most part the Five are just using the same old tricks with the same old powers and limitations. We've seen the Titans grow, we haven't seen the Five do the same.
And Vic's a Fourth World demigod now. DC acts like the only thing that did was let him open Boom Tubes, but if they gave a **** and wrote this to its potential then Vic has seen a power upgrade well beyond anything any other Titan or Titan villain has seen (except maybe Wally). Vic should be operating on a Superman-like scale and scope now, and the idea that he needs the old Titans gang to handle the Five is sort of like Superman needing the entire League to take down Toyman. It's overkill. But with Vic on his own and the Five focused on him instead of having to split their attention between Titans, they have a chance of being dangerous; they've got the numbers advantage, their combined powerset means Vic has to deploy multiple countermeasures to contain them....it could strain Vic's abilities if he's on his own, and you could get a good fight out of it with real stakes in a believable way I just don't think you can accomplish with the full Titans team anymore.
But I'm a big advocate of the NTT being written as more competent than DC usually allows. If I had my way, most of the old Titans villains would be given to individual Titans now; Nightwing would be handling the HIVE on his own, Vic would be dealing with the Five himself, Kori would be taking on Gordanian invasions single handed, etc. I want to show that the NTT aren't kids anymore, that they've grown up to equal (if not surpass) their mentors. And if they still all need help to deal with threats they faced as kids? They don't look very competent or improved, they look like they stalled out in high school.
I mean, nobody is going to accept Wally West struggling to deal with the Mad Mod right? Wally became (much, much) faster and more experienced and learned new things and we wouldn't believe that the Mad Mod is a legit threat to him now like we would when Wally was a kid. So why is Vic any different? He should be one of the most powerful beings in the universe now and the idea that he still needs help to deal with a group like the Five? I just don't buy it.