To me support ships ain't dealing any damage, because it's quicker, cheaper and more efficient to send a bomb taxi into the battlefield than having strike craft jump back and forth into and out of action..
The "cheaper" being the most important part, as the GTS and GVS don't have gun mounts, don't have capacitors to power them, or a power supply to charge 'em up, they don't have afterburners, no shields, no missile tubes and as such probably no advanced sensors/guidance systems or electronics on board other than comm and nav.
What they do have is the ability of a single ship keeping several in combat for extended periods of time at the cost of a single jump drive being used from time to time when the supply ship goes to resupply itself.
A similar thing would be with modern flying tankers (a play on the original post: Why not give them bombs, missiles and CIWS turrets and get rid of all the fighters they support, they have the fuel to reach everywhere so what's the purpose of the dedicated ordnance delivery units?).
The thing that I wonder about is how many Ursas could that thing resupply? There is no limit in game, but physically there must be a maximum number of warheads that thing can carry.