Raikiri is one tech- an enhanced and concentrated form of chidori. Kakshi made it in an attempt to add his element lightening to the rasengan. Minato pointed out it's draw back - the tunnel vision which could be overcome using sharingan.
Not being able to use raikri or chidori doesn't mean not being able to lightening at all. It doesn''t stop him from using mini rasengan either. It simply means he cannot mix his element with rasengan.
Yes, he still has his raiton affinity.
My issue here is not that I think this restricts him using raiton, my issue here is that the person writing this novel didn't actually do his(I think it's a he, anyway) research on Kakashi or the technique.
Minato's warning about the technique was in regards to Kakashi's speed when using the technique, he was going too fast to react to anything his opponent might counter with:
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Kakashi has shown in the manga ways around this problem, as well as shown alternate uses for raikiri as well:
Using Tsugia to pin the opponent/eliminate the risk of a counter:
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Using it as assassination technique/taking the enemy by surprise:
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Using it as a support technique:
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Using it as a defense:
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Among other things.
I'm simply disappointed in the early news/reading of the novel. Hopefully the rest of it is better than it's beginning, but a flaw like this at the start doesn't bode well for it, nor does it do well in educating fans of the uses of raikiri.