I do like to use planes over bombers and transports, but thats only since i maxed them at atomic lvl.
At least now they wont die so easily.
What i find terrible about planes, is that they almost never take the 'designated' path to the target, they make large circles from the target and if you are so unlucky that the target is destroyed before your planes get there, they just circle above enemy bases looking for another, not designated target.
On top of that, planes are a pain in the butt rebuilding, with no way to speed up the rebuild.
what i would expect from the planes is that they go to the target the shortest way, attack it, make a small circle (like the bomber behaviour) and get out of there. If a target gets destroyed, i want them to return home. Only in that way i can take control over my attack and use them way longer during an attack. During looting (i loot bases that are easy for me), i dont care, but during wars (i attack ppl my lvl and higher), using planes are a pain cause even my fully upgraded planes wont last much longer then 1 strive (mostly deep into territory for targets like silo's) and thats mostly due to those large circles and 'wondering around'...
so yes they are helpfull (more then bomber/transport), but they surely do have their flaws which musnt be ignored...