Dragon Ball Super proves that Frieza will always be Goku's greatest enemy. The story that made Frieza relevant again included a detail about Frieza's power that ensures the villain's status as the biggest threat to Goku and Universe 7 will never change.
In Dragon Ball Z's Frieza Saga, Frieza was introduced as a world-conquering mass murderer whose power knew no match. Vegeta, Piccolo, Gohan, and Krillin managed to push him into achieving his Final Form, but none posed a significant challenge to him. It wasn't until Goku arrived that Frieza realized that he could be beaten. After becoming a Super Saiyan, Goku finally defeated Frieza. In canon, Frieza didn't emerge again until the Golden Frieza Saga of Dragon Ball Super when he returned to get revenge on Goku. He also appeared in the Universal Survival Saga as a reluctant ally, before going back to being a villain again in Dragon Ball Super: Broly.
In the world of Dragon Ball, most villains are forgotten after being defeated by Goku and Vegeta. That's because it's the nature of Dragon Ball for the heroes to grow in power as the series goes on. For instance, Dragon Ball Super's Yamcha, Krillin, and Tien would likely defeat many of Dragon Ball Z's strongest enemies with ease. This makes it hard for any villain to remain relevant, but Dragon Ball Super makes an exception with Frieza.
In the Golden Frieza Saga, Frieza is levels above Gohan and Piccolo, even though both should now be able to overpower him. After all, Frieza only trained for four months after being brought back to life by the Dragon Balls. This is an extremely short length of time, compared to the years that the heroes have spent training since Frieza's death. So how can Frieza be strong enough to enter his "Golden Frieza" form and force both Goku and Vegeta to go Super Saiyan Blue?
It's explained that Frieza's power in the Frieza Saga was all natural. At that point, he never needed to train. Frieza is such a powerful being that it only took him four months to reach a level that has taken Goku and Vegeta years to reach. Frieza's potential outshines nearly every character on the show, which is a notion that should weigh on Goku's mind. All Frieza needs to challenge Goku is the proper motivation and just a few scant months of training. This means that no matter how strong Goku becomes, Frieza can always catch up.