A New Hope would have only been moderately successful at best without the combination of David Prowse doing the physical work and James Earl Jones voicing Vader. Possibly a flop.
Yes, the rest of the cast was solid and it would have still been a good B movie without them, but the voice and physical presence of Vader set the tone of what the protagonists were fighting against. Vader isn’t the best character either! In fact he is a one note villain in A New Hope.
The combination of both actors was the secret sauce that set the foundation for the entire series. Heck, Vader overshadowed Palpatine in their scenes together for me, even with Ian McDiarmid’s excellent performance.
No, the whole point of the original trilogy’s framing of Solo was that he was a terrible person who because a better person. Having him be a decent person first undermines the character growth in the same way as the retroactive change to have Greedo shoot is why people don’t like that part of Solo.
I don’t dislike Solo as a movie, but it didn’t serve his initial characterization.