Not that Solo was a terrible movie. Personally I fee as if Solo was a solid entertaining but feeble effort, in the same sense as National Treasure. Not terrible, but a worthy adventure film if you're having a boring night. So it's deserved of its 6.9.
The Rise Of Skywalker though is rated 6.6 on imdb as of this time. Yes it's a stinker of a chapter in the franchise, but it seems unanimous now that it's destined to be ranked lower than TPM.
I don't think words like "stinker", "destined", and "unanimous" mean what you think.
For starters, it's ranked higher than TPM at IMDB, the source you cited. Barely, but it is. All three movies have virtually the same score at IMDB. It splits the Metacritic score with TPM. And of all 3 sites, it has the highest of all 3 movies with fans.
The Phantom Menace
6.5 at IMDB
52% & 59% at Rotten Tomatoes
51 and 6.1 at Metacritic
Solo
6.9 IMDB
69% & 64%
62 & 6.1 at Metacritic
The Rise of Skywalker
6.6 IMDB
51% & 86%
53 & 4.6
I was pleasantly surprised how much I enjoyed Solo. I resisted seeing it, but went to the theater the last week it was out and honestly loved it. I thought it was good fun.
That movie had good fan reviews from the day it was released. A lot of fans hatted TLJ and preferred this one and it's been that way since fans were allowed to rate it.
I heard that Disney forced RT to COPY the TFA score to the TROS score, to make it look more popular with critics than it actually was, to encourage audiences to go see it. Extremely underhanded tactic, if you ask me!