Thank you for your feedback!
The main reasons for not including a built-in radio button validation are exactly the ones you mentioned - performance and the necessity of adding the required attribute to each element in the radio button group. I would encourage you to submit this as a feature request at KendoUI UserVoice
so we and other members of the community can evaluate, comment on and vote for it. Most voted requests are often included in future KendoUI releases.
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