Without question. Killers have gotten a lot smarter than back in the day. Lots has changed, murder rates have gone down a ton, but so have the clearance of murder cases by police. There's a lot of factors at play with regards to all that so it's not completely clear cut. More would be serial killers are likely picked up earlier for their initial crimes and murders and are in prison preventing them from doing further harm, but there's still a lot out there that haven't been caught because they're smarter and more careful.
Samuel Little was active well in to the late 90s and not caught until 2012. LISK has not been caught and could in fact possibly be two different serial killers active on Long Island, as well as responsible for other killings across the US over the past couple decades.
I think people vastly over estimate the ability for law enforcement to solve crimes. It's one thing to kill someone you know out of passion and purpose and get caught, but it's another when you literally have no connection or ties to the victim and you literally travel from out of state come in kill someone and then leave without a trace. There may be lots of cameras and shit around these days, but they're not everywhere and people like sex workers, undocumented immigrants and just minorities and poor people in general are still extremely vulnerable.