If a tactical bomber manages to pick off 1 material, its already a good buy relative to fighters. Trucks end up being exposed fairly often, and even if a tactical bomber isn't hitting the enemy, it could be because its forcing them to move their units differently.
Its not a value unit (fighters are the value aircraft), its a tactical unit. It can force your opponent to do things they don't want to do or kill key units that disrupt an opponent's plans. I have a very distinct memory of taking Moscow only because I bombed away its free material two turns in a row, thus stopping fortifications from being built.
Those tact bomber techs do seem really weak to me though. Since everyone is going to pursue improved fighters pretty much every game, the tact bomber ends up competing against a unit which is improved by tech, while investing in tact bomber techs seems really questionable to me.