Complex sentence: Redirects from related words are not properly redirects from alternative spellings of the same word but, at the same time, they are also different from redirects from a sub-topic, since the related word is unlikely to warrant a full sub-topic in the target page.
Split into simpler sentences: Redirects from related words are not properly redirects from alternate spellings of the same word. But at the same time, they are also different from redirects from a sub-topic, since the related word is unlikely to warrant a full sub-topic in the target page.