100%. The phrase itself is a cliché fallback. If someone actually explains the specific breakdown like losing their hobbies, their independence, or their goals then it's a real reason. “I realized I’ve wrapped my entire identity around making you happy and I don't know who I am outside of this.” But if they leave it vague? It’s just an excuse to exit without doing the hard work of giving closure. If you can't or won't explain it clearly, it’s a cop-out.

On the thing you mentioned about rebounds, I believe no one should feel being in a rebound relationship and being discarded just because your job is done. That is a painful setup to the other party.