Yes, Real Madrid does need a striker, not only as a back-up for Benzema but a great player who can play alongside Benzema. In the latest news, Real Madrid has made a £137m offer to PSG to sign Kylian Mbappe. If this offer is rejected, PSG will waste big money because Kylian Mbappe's contract only has a year remaining and it seems that Kylian Mbappe has no intention of extending his contract at PSG.
Real Madrid also desperately needs a center-back and I think Real Madrid should buy a center-back first and then buy a striker. Conceding 3 goals against Levante is proof why Real Madrid really needs a superb center-back.
With the personal pressure from Mbappe (reject to renew his contract with all offers from PSG), the odds that Real Madrid have Mbappe is increasing. Especially when Manchester City can not buy Harry Kane.
If PSG sell Mbappe, they will have two strikers to choose, Kane and Ronaldo. Kane is better because he is younger and will have longer career than Ronaldo. But Ronaldo has a cheaper cost and PSG can use rest money to do other things.
Kane probably won't leave Premier League so the scenario with which Ramos, Ronaldo, Messi reunite all in PSG is very possibly.