I'm surprised at your interpretation of the other person's comment. What they're saying is that a rebound relationship is a disservice to both characters. No one is saying she can't find love or happiness again. She just needs to process her grief first because she is clearly still not over her dead husband. She isn't ready for a new relationship right now.
You're overreacting way too much
You're arguably providing a rather generous interpretation of what that other person said as well, if I'm being honest, given they said none of the things you yourself are claiming.
Yes, a "rebound relationship" would be a disservice, but that's
your take, not the original commenter's. They just said Otakei being "a replacement" didn't sit well with them, with no follow-up.
Insults are unnecessary, but the last several chapters have had similar comments that have similar senitments in far less graceful terms. Some people seeing more of the same, even if less vitriolic, and interpreting it as such, isn't a stretch.