Aguero will be gone in 2 years and we aren't winning the Champions League with our current set of players unless the forwards improve in front of goal in high leverage moments. I do think Sane and Jesus can become what we need but just calling it as it is, we don't have the consistency up top to beat the elite sides and unfortunately that includes Aguero at this present time. Aguero gives me the most faith to step up in big moments but he doesn't always mesh well with the way Pep desires so it's a catch 22. The one player I'd want in front of goal at this present time in a big moment is De Bruyne. And regarding a player to replace Aguero, I haven't seen someone outside of Neymar and Messi like you stated who could mesh well and be replied upon in front of goal. Kane would be reliable in front of goal if given the chance though but not sure if he'd fit in overall. There's a few other potential outsiders but not seen enough in big moments to say for certain. Dybala, Mbappe and Griezmann.