I honestly agree with the arguments they made to defend it, but then they tied themselves in loops trying to defend things like separate Greek and Cyrillic scripts and making superfine distinctions about how that isn't the same phenomenon. But they couldn't merge those scripts together now even if they wanted to, because of the stability policy. And the existence of the blackletter, small-caps, superscript, etc. characters seems entirely indefensible to me. All font rendering issues; it's clearly the same symbol with the same fundamental meaning.

Really, they needed to come up with the idea of variation selectors way earlier, and use them aggressively. And design something more consistent for character composition, and skip the precomposed characters (those really are glyphs representing a cluster; being able to treat the cluster as an atomic entity versus its components doesn't add actual semantic information to the text).