Purodha,
Redirects are cheap - so cheap in fact, that they take up more space when you delete them, so even if they are misspelled or whatever, they are mostly left to rot unless they break something (for example when someone wants to use a redlink like [[redlink]] and someone else makes a redirect for "redlink"). I don't think there is any Wikimedia project that actively deletes redirects.
In general, redirects are supposed to be used as alternate names for the same thing, and in Wikidata, this is done by typing in alternate labels. Of course people also use redirects as a way of "bundling concepts" - just take a look at all the redirects to the article for "insurance" for all the types of insurance that don't yet have their own article.
Before Wikidata there were lots of interwiki links to redirects, and this caused multiple issues with unresolvable interwikilinks. Wikidata was invented to be able to use persistent identifiers for Wikipedia articles. Now everyone is surprised that now the interwikilinks work differently from before. The fact that redirects are not supported is by design and not a bug. Going forward, instead of making redirects, Wikidatans should just keep creating items in Wikidata and let the Wikipedias take care of themselves by letting them create articles and redirects in the normal wiki way. It should not be a goal for Wikidata to sitelink to every redirect in every Wikipedia, just as it is not a goal to sitelink to every image on Wikimedia Commons.
The subject at hand in this email thread is that instead of creating an article, the user ThurnerRupert made a redirect in the German Wikipedia called "afrikanische Pflaume" that links to "Prunus" and expected to be able to interwikilink this redirect via the Wikidata item for "African Plum" to the French Wikipedia's article for "safou". I would say that Wikidata should not support this workflow and it is incorrect editing behavior. This has nothing to do with the numbers of redirects or whether or not they need to be deleted by anybody.
Jane