Tractors lower the BD of ship, but its not an issue. Issue is immobilize and raid (for AI you can add neutron blasters to capture). Problem with tractors what at turns when they arrive, beam ships doesnt have enough power to have 1:1 shoot-kill ratio, and tractor ship do have. The single real alternative to them is emg (emg ships have 1:1 ratio too, but you can paranoidily have a antimissile defences, and stop them, but there is nothing to stop tractors at all).
You never saw problems with fighters or missiles because you probably never played a game involved optimal strategies (i had read this forum alittle, and as i got you play AI mainly, and in very suboptimal way, so probably thats an answer). Problem with those techs what game have no chance to last long enough to "Higher tech" arrive. At the moment the fighters arrive, there is no tech to stop them yet. They are cheaper than lasers in research and build. In fact in most multiplayer games there is added a special peace rules of some sort, to make game last long enough, so there is need in building colonyships, teching supercomputers etc. Otherwise the only techs you need to bother to research is fighters, deuterium, fusion beam and best drive you can get (usually fusion only). And, problem is what you never can learn how to actually defend against them playing VS AI, it cant fight at all. In case you interested in this game, and want to improve your level, i posted a link already. Dont plan to sound bad, but there is alotta to learn still (in case you're honest in posts here).
upd. I will add an easy example explaining incorrectness of this ""I dont find this useful", "I dont see any problems with" etc" approach. Suppose thats about Guardian, and you say "I dont find EMG DD's useful, i dont see any problem with my usual way of 20 plasma cannons titans to kill a guardian, it always work and im fine (its just example, i dont mean you actually think this way about it)". But. Even if you somehow still dont know how to kill guardian right way, or not belive it, it lead to 2 alternatives: you decide to no bother to learn it, and miss alotta from a game you play, thus making the fact what you actually asking and answering question about it weird, because that should mean what you suppose what some players know game worse than you, and what you can effectively help them get better, while prefer to miss that for yourself; and second alternative - you want to actually check a new data, you trying it on your own, or look some video etc, and realize what indeed, 20 plasma titans simply worse than 8 early destroyers. Because in any actual game 20 titans strategy will lose to 8 DD's. Ofc you can also think "but im playing AI, AI is very easy and dont need to play good from my side". That true, and after you get how to do it right way you can go back to 20 titans, or 1 ship with stasis etc. But, you will know how to do it right, because you didnt missed an opportunity, and if you will need to do it right, you will be able. And also, on general note, approach "i dont need it vs AI, my games are simple" make ANY advice and questions and answers about game pointless, you can get a question, "i cant win that dumb game, coz AI cheat, i play it my usual way, put all into farming for 200 turns, and then start research, but AI cheat and i always lose!". You can try to share your knowledge about optimal way with him, and get answer "i dont care about boring strategies, i like to play it the way i play". But you see, while there is nothing bad in it, there is no point in posting a question then. As you see its pretty wide topic, even one hypotetical example, and there is much more, fighters\tractors is very easy to get, economic could be much harder.