My point is not that it isn't balanced. It might be, it might not be. But I would say the same thing if it was perfectly balanced. Or given a 2+ RA save and an invulnerable save and TRA and was balanced perfectly. My understanding is that Terminators are the toughest thing in a marine list, yes I know they can teleport, and get a chaplain and all that. Vindicators get walker but both they and preds have the same armour save so I would say they had comparable armour?
If you are saying that terminators are no longer the toughest infantry type in the marine chapters, that a centurion has as great a chanch of surviving a multimelta as a terminator, fair enough. Then procede to balance them. Perhaps in that process you would think they add little as an independant formation and try them as an upgrade to replace dreadnaughts, etc etc.
But if they are not meant to be as survivable as tactical dreadnaught armour, no amount of balancing will help. So I am quite prepared to beleive GW has reversed all its fluff to date about terminators being the toughest marines, I just don't know that because I don't follow all the new crap GW puts out in its codex. So I assume they are as tough as terminators (assuming a mix of normal and storm shield guys)? Same chance of surviving multimelta, lascannon, or plasma hit?
Seperately you also have the question of what do they bring to the list, something balance doesn't help with either. I am not sure what role they are meant to fill (terminators are heavy armour assualt infantry, assault are naff assault infantry, bikes are better than ass marines assault infantry, then you have devs, preds and raiders as firepower), currently they don't measure up to terminators at a similar price point but look they replace devestators. Both have 4+RA from the fortifications, but they have a better (first strike) FF and twice the firepower for 50 more points and are far better if you have to advance out of the fortifications. Again they could be well balanced, but if they don't have a clear role, why take them? Unless the planned role is to replace Devs?
To be honest other than a broadside equivalent which would step on dev toes less, or a tough upgrade to a infantry formation to replce dreds, I am hard pressed to think what role they could usefully fill and would have thought the garrissoned firepower could be better done for the list with a formation of 4 hellfire dreds for 200 points (which would also be better for model collections).
So basically just looking for you to say, yes they have been installed by GW as equal to terminators in survivablility and here I intend them to fill the following function (replace garissoned devs, be a formation to take back fortifications, etc, etc). Test them for their ability to fill x role.

(On Tau Broadsides I beleive they even used to have a note on them as FW sold them modelled 2 to a base - only the general shortage and expense led to people doing them 1 to a base - saying yes they can be mounted more than one to a base, but are still light vehicles.)