I have a GCC whose toes go the wrong way when she perches and she generally keeps her foot fisted when she walks around on flat surfaces. I have a wide variety of perches - natural branch type of varying sizes (she prefers larger ones as opposed to skinnier ones, easier to grip), platform perches, and corner perches (where there are several dowel perches at a diagonal).
She was very skittish about hands when I got her, so she learned to jump up on a balled up towel before we worked on jumping into my cupped hands. Then I flight trained her after her feathers grew back in, so she flies on command to her hang out spot and cage. She doesn't have a problem landing on flat surfaces or the side of her cage. Trying to land on perches is too difficult as she can't always get her foot open correctly to land. Flying helped her tremendously, her confidence shot up.
As for hands, when she first started flying again she crashed a lot, and she got in the habit of me plucking her up from behind, so she'll also let me pick her up that way (just back straight up into my open hand and grabs my finger under her with her good foot). She'll step up into a cupped hand ok now, too. If you want to stick with stepping up on a finger, I'd suggest using your other hand to kind of shelter her while you're moving, sort of like you'd put your hand around a candle flame to keep it from going out when you're moving. I had an older bird with arthritis and missing toes that had grip problems. She preferred stepping up (it was how she was trained before the toe issues or arthritis), but the protective hand was something that kept her steady so she wouldn't fall.