Dragon Ball Super's Master Roshi power level retcon is a major problem for the anime, because of the questions it raises about Roshi's role (or lack thereof) in previous Dragon Ball stories. In the lead-up to the Tournament of Power, Dragon Ball Super reveals that Roshi - a character who has been on the sidelines for years - is much stronger than anyone ever expected.
The seemingly immortal Master Roshi was treated as a formidable fighter in the original Dragon Ball anime when he became Goku and Krillin's martial arts instructor, and his skills allowed him to remain relevant for quite some time, but by the time Dragon Ball Z rolled around, the Turtle Hermit was no longer the asset he once was. Due to his perverted nature, the anime kept him around as a source of comedic relief, and as a character who could provide advice when needed. Roshi was elevated to a slightly greater level of importance when he joined in the fighting during the Golden Frieza Saga, and became a member of Goku's Universe 7 team for the Tournament of Power. Roshi succeeded in defeating three contestants from Universe 4 before becoming the third Universe 7 fighter to be eliminated.
Prior to the Tournament of Power, Goku and Tien have to deal with a mind-controlled Master Roshi, who easily bests Tien in combat. Roshi also succeeds in posing a challenge to Goku in his base form. Goku prevails over Roshi, but learns from their fight that Roshi has been hiding his true power all this time. Goku realizes that Roshi has been secretly undergoing intense training when no one else is around. What this means is that Roshi is much more powerful than he appeared to be, and it's not clear how long this has been going on.
Based on what was previously shown, Roshi gave up on being a serious fighter prior to Dragon Ball Z, which would mean that he shouldn't even be capable of defeating the Saiyan Saga villains, but in Dragon Ball Super, he accomplishes the impressive feat of defeating Tien, who at this point should be on the level of Cell, or perhaps even higher. It's unlikely that Roshi received such a massive, sudden upgrade, so it's more plausible that Goku's assumption about Rosh is correct: he had to be training in secret for a great deal of time - and quite possibly the entire time.
If Roshi didn't give up his training, then why was he content to do nothing during Dragon Ball Z? Admittedly, no matter the state of his power, he couldn't have been much help against Majin Buu, but he could have joined Gohan and Krillin in the mission to Namek in the Frieza Saga, or he could have participated in the fights against Nappa and Vegeta, the Androids, or Cell and his minions. Though it's true that he might not have made a significant contribution, if he was keeping in pace with heroes like Krillin, Yamcha, and Tien, he could have at least made a difference. Unfortunately, Dragon Ball Super doesn't provide a satisfying answer to any of these questions.