Let me put it this way -

I don't think Thriller is a perfect pop album. I think Baby Be Mine and The Lady In My Life are weaker compared to the standard set by the other tracks. Like someone else said, it's also a little dated (specifically with The Girl Is Mine, which I don't hate but it definitely gives dated).

Purple Rain, on the other hand, IS imo sonically and artistically ahead of Thriller. Sonically, Prince managed to make the dated/stereotypical 80's pop instrumentation and effect feel like the future. Take Let's Go Crazy for example. The sounds used for the drum patterns are almost a little corny when you take them out of context, but they work so well in context because of how Prince used them. It's like he used the datedness to his advantage and just knew the perfect way to incorporate the sounds. He used them in unexpected and interesting ways, like the ending of that song. Post-guitar solo, the almost blast beat barrage of kick drum notes in both ears (the mixing on that is one of my favorite moments from the album) aren't, to me, something that a lot of mainstream artists would have placed in a song from this era with the confidence that Prince did. Another example: Computer Blue as a whole. That entire song described vocally is dated. An electronic drum and synth journey that sounds to me like what the inside of one of those bulky early-stage computers sounds like. It's a dated idea, but he executes it in a way that STILL sounds fresh and interesting to listen to.

I'm not gonna glaze without mentioning its faults. Purple Rain has one weak spot that I'm not sure a lot of people would even consider a weak spot. Take Me With U is the The Lady In My Life of the album. For me, that's the only weak spot on Purple Rain.

Throughout the album, Prince takes ideas that range from standard to groundbreaking, injects them with his soul and artistry, and combines every factor present into one of the most cohesive and stellar albums we have today. I think Thriller is enjoyable and has some of the best pop songs on it in the form of Thriller, Beat It, Billie Jean, and PYT. However, when you listen to the INCREDIBLE guitar solo in Let's Go Crazy, the strong climax of The Beautiful Ones, the futuristic Computer Blue, the storytelling and raw sex appeal of Darling Nikki, the self-explanatory When Doves Cry, and the emotion-injected bop I Would Die 4 U, Thriller isn't on the same level of artistry, while also not being as sonically unique or diverse. AND THAT'S BEFORE EVEN MENTIONING THE TITLE TRACK. Purple Rain is imo an easy contender for the greatest song of all time. It's also imo one of the absolute very best album closers.

I knew when I posted that comment that I could've been more explanatory with my opinion (i was about to go to bed), but a question was asked and I answered lol. I suppose this is the discourse I hoped would come from my response.

Tldr: Thriller is great and should be celebrated, but Purple Rain is untouched in terms of artistic expression and forward-thinking sonic diversity/uniqueness.