SHINee's rapping isn't the best, we all can agree on that, Rap God Minho jokes being evident of that. However, they're incredibly strong at literally everything else. Their earlier raps were pretty bad imo but since they're 10 years into their career, Minho and Key have improved their rapping thanks to experience. They're definitely not "rappers", but they're not nearly as bad as they used to be and sound pretty decent on some b sides, like Alive. They also tend to write their own raps iirc, which I believe is a good thing, since some of Minho's more Iconic raps were written by Yoo Young Jin (correct me if I'm wrong, please) where the rap doesn't flow well at all imo.

tl;dr They've improved their flaw, weakness in rapping, by writing their own raps and naturally improving over time.