That doesn't mean that sd version is evenly low cost branch but they get those updates first. Is Chinese people so crooked that you can blame product price to ****** update service when almost same price range sd version get that update when you can call it update up to date.
But it's old, slower than MTK version. Same price but already obsolete, or low-end. Of course you can wait longer to by a device that is already low-end.
This kind of thing happens with every company - buy a device at the wrong time, 2 weeks later a better model is out for same price.... Nothing unique to Xiaomi or MTK.