Well, a few things come to mind:
- 15pts isn't really a throwaway amount, if you see what I mean - especially for such a small squad.
- The Sybrite is basically wasted beyond the haywire (the squad is so small and fragile that Ld is basically irrelevant).
- The Haywire grenade has barely 1/3 of the range of the Blaster. Blasters are awful weapons, compared to meltas (despite costing 50% more). Literally the only advantage they have is that they have more range... and this tactic means sacrificing even that small crumb of benefit.
- Also, if you're going that close, you're basically making them a suicide squad. And, if I'm going to do that, I want a suicide squad that's better at it's job. No point in throwing away 70pts of troops (probably their transport, too) just for a single blaster shot and 1-2 throws of haywire grenades.
In addition, I think we just have better options. If you want more anti-vehicle stuff, there are Trueborn (who can have 4 blasters), or Scourges (who can have 4 Haywire Blasters or 4 Heat Lances). It just seems more efficient to keep troops cheap, rather than trying to mix and match weapons with different ranges.