You are correct
You can certainly get more than 250 from TPI. You can order a bigger intake and bigger tubes (or go mini ram etc.), add a bigger throttle body which means you will also want to add bigger injectors (to handle the flow). But man is that stuff expensive. 1500 for complete fuel injection (ok maybe not complete depending on what system). And then theres setup. Compare that to a Carb (300), Distributor (110) and sorting out the fuel (use stock fuel pump with pressure regulator about 100bucks) and of course the intake.
Again, nothing wrong with EFI (TPI in this case) except when you deal with a 20yo wiring system and the cost of some of those parts, phew. It is still less expensive to build power using "conventional" means.
But, if the thing runs good and you arent' worried about doing big mods, the stock system is fine. Replacing a bad injector is certainly cheaper than replacing the whole induction system. Just depends on whats wrong with the car, and what you want to do with it.
TPI cant be the best thing or chevy wouldn't have gone to the short runner manifold on everything since the L98. (think about it, tubes that cover the injectors, everything is under the plenum chamber, no room to work, ugh).
For that matter, if you have the pesos, dont screw around, buy a used complete LS1 or 2. That's a sweet setup.
Anyways, as the saying goes, to each his own....