Your regex will fail in all, but the most trivial cases. It fails when < is used to not start a tag, and it fails when > is used inside an attribute value, or inside a comment. If you have to do it with a regex, use something like (untested):

s{<[a-zA-Z][^>'"]*(?:(?:'[^']*'|"[^"]*")[^>'"]*)*> # Tags
 |<!(?:--[^-]*(?:-[^-]+)*--\s*)*>                  # Comments
 }{" " x length $&}xeg
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