Without question, but the circumstances would be vastly different.
Without Heyman, there would have been no reason to initially care about Lesnar, and that connection would have taken a while to be established. With Heyman, we had someone who was an established heel character, who gave the fans a reason to care. That sped up Lesnars development on-screen tenfold. We all know that Lesnar isn't the worlds best talker, and especially in his early days, that would have hindered him. Solution? Give him a guy that could sell chicken to a vegan in Paul Heyman to talk for him, and instantly he has a better chance. No guarantees, but a chance.
Of course though, just look at what the guy is capable of. When he first debuted he tossed Mark Henry and Rikishi around like rag dolls. He decimated lower-card people, destroyed a top tag team in the Hardy's all by himself. The first guy to show him any competition at all was Rob Van Dam, and he pretty much got crushed. The speed he moved around the ring, combined with near-unrivaled strength and a wrestling ability to match Kurt Angle on his best day; there's no way in hell that talent is not gonna progress.
Would his lack of ability on the mic hinder him? More than likely, but it would have only delayed the inevitable. Lesnar was, and is, a freak of nature. He was always destined for great things, and it's just a shame that he left when he did. Without question, had he stayed, he would have been the biggest star WWE has right now.