It's not that he has no sincerity. It's just that he still lose to LHL's skills in faking sincerity with that 'suffering monk' facial expression. All this takes time to learn.
Initially Dishonorable Son also appears damn cocky in his first national day speech but later likely he went through some grueling training by an image consultant to create a fake persona that looks like a suffering humble wise monk. After realising that the trick works very well in helping PAP win elections, he then start to take on that persona and deceive naive Sinkies til this day, LOL.
You can see here how this CBkia master it to perfection. LW still got a lot to learn: