Well no sergeant options will prevent people from adopting them wholesale. Now that Assault Intercessors are getting Hammers and all the options especially.
I think you might be right. If I'm honest, I'm a bit unsure what I'd do with these guys. The problem is that normal intercessors are just so good, and much more effective in melee.
A unit with the not-stalkers might be good. But really, I could well end up using some other unit to hold backfield objectives. These guys just aren't all that shooty for what I expect them to cost (130-150 for 5). Normal Intercessors are already tanky rather than shooty and I think these guys will take that to extremes.
Their main strength might be having 3 wounds in a meta designed to deal with 2 wound targets. They're very substantially tougher than Intercessors, for this reason. 40mm bases will make them harder to hide, but that's probably ok.
Ultimately it's all going to come down to how much these guys cost. They could potentially just replace Intercessors as the best all-round troop choice, or they could end up not really being worth their cost.