Right, but will they be able to say that the customer was thrilled with their rewrite? Probably not; they're already mostly happy with the simpler site and now

Right, but will they be able to say that the customer was thrilled with their rewrite? Probably not; they're already mostly happy with the simpler site and now they've paid to make things (almost certainly) more complex than they need to be. They probably feel swindled into agreeing to a rewrite of something that was mostly working but The Next Developer told them that adding that new feature would require completely rewriting the front- and backends.