Your proposed stingray refit was 32 industry, because you assume upgrading to entirely new Phase cannons somehow won't mean making new ones and so only cost 1, when realistically we would pay full cost making it 35.
5 more than this ship. Which also gains a rear facing cannon.
That leaves out the increased maneuverability,
And no, as far as I'm aware the photonics aren't able to just replace atomic and spatial, its an entirely new launcher.
The biggest increase in both offense(besides the photonics) and defense is the improved maneuverability, letting it bring its weapons on target and avoid incoming fire.
Your proposed stingray refit not only costs more than this ship, by atleast 2, more likely 5 or more, it is just as much of a death trap as the original.
Actually it would probably have a much lower survival rate. It would just draw more fire due to its better weapons, while still being the same at avoiding it.