As someone who’s watched seasons 1-5 as well as Fate, I’d say that while the OG Winx are stronger, they’re fairly evenly matched.
For those who haven’t watched Winx Club, the reason they’re stronger is that the OG Winx have a larger array of forces to control (they can control earth, plants, tech, fire, water, sound, light, sometimes air, and whatever Morphix is), the abilities to levitate stuff and instantly create shields, as well as, you know, fly. Heck, they could even use their Believix powers to change their enemies’ mental state if they wanted to. Not even Fate Musa can do that.
However, the OG Winx usually serve as kindhearted protectors who fight for the safety of their realms and very rarely fight with the intention to kill. Otherwise, let’s be real, the Trix wouldn’t have made it out of season 1 alive. The Fate Winx are less sympathetic, as shown when they literally pushed Beatrix into a trap in order to free another criminal. It really comes down to where they are and why they’re fighting.
TL;DR: The OG Winx are stronger but the Fate Winx can be meaner, so they’re pretty evenly matched.