Quoting two relevant posts on why I think Sonic has stayed popular and why it's doing better than Detective Pikachu from the other thread:
Sonic has stayed relevant for a few reasons in my eyes.
01. Sonic has an incredibly appealing design. One of the smartest things Sonic Team ever did was make a design somewhere between cool, cute and simple so it'd be easy to draw for kids. A lot of kids can just see Sonic's design and want to know more about him. I sincerely think a big reason the Sonic brand has stayed so alive for 30 years is because of Sonic's character design.
02. Sonic has had successes outside of gaming. Sonic Boom was surprisingly popular with kids, Sonic was in both Wreck-It Ralph films, Sonic is known by kids by Youtubers and the like as well who do gaming stuff, the Sonic comics were for a long time the best selling kids comics, Sonic X recently has been popular on Netflix on their top viewed stuff and been sitting there, Sonic merchandise is available in places. Sonic's cartoons have proven popular, again Sonic Boom on Cartoon Network popular, Sonic X on Netflix is doing great numbers too, etc.
03. The older games are still present and plenty of parents still have Sonic games for their kids to play. Plus the newer games haven't been bombs specifically either, just there's been a lack of recent Sonic games in the last 8 years. I think honestly there's probably kids who play his older games for one reason or another. The mobile game downloads for Sonic have also stayed very high, Sonic's found success on mobile. You also can play most older Sonic games on like every streaming game platform, on a lot of mini-consoles, etc. Also all of those Mario & Sonic Olympics games did pretty well.
04. The internet. I kinda' touched on this in point 2, but I need to emphasize Sonic has a presence online. Almost everyone on the internet knows who Sonic the Hedgehog is, Hell I say "Almost" since I feel not everyone can, but I've never met anyone who had no idea who Sonic was. Sonic memes, Let's Plays, cameo appearances, fucking ice cream bars, Sonic I think might've actually been saved by his presence online and just in various outlets in pop culture because everyone fucking knows who Sonic the Hedgehog is. Add to that he has an appealing design and things in various fields to check out, and I think that's part of how he's stayed relevant. I think people making jokes about Sonic and memes, people "ironically" or unrionically doing Let's Plays of his games, Sonic being a character who often comes up with video game discussion, his presence in the Super smash Bros games, his cameos in everything from Wreck-It Ralph to Hatsune Miku stuff, has kept people knowing who Sonic is, and I think becoming aware of him kids may then see he has a cool design and go check out stuff he's been in. I think that's honestly the core of what's been happening, Sonic continues to be talked about and appears in things, and he has an appealing design that leads to kids finding him.
I think a few aspects that benefit the Sonic film also:
-Detective Pikachu kinda' undersold itself because it comes off like a spin-off with the concept, like it doesn't seem like a "core" Pokemon movie. The Sonic movie I think comes off pretty simply it's "Sonic the Movie". I don't think Detective Pikachu came off as clear to casual audiences it was "Pokemon the Movie". That does mean something I think to audiences the sorta' weight to a film.
-Detective Pikachu I'd say isn't as much of an "All-Ages" film, it is technically but the content within with the crime noir events going on isn't quite as appealing to children. Sonic meanwhile I think more clearly is a film for all ages, helped a bit the plot premise is similar to some other children films in the last decade, and I think has more in it that children and adults can enjoy. It's appealing to a broader audience.
-Jim Carry. This is his first big role in years, many have affinity for the actor. I know a lot of older people who are checking out this film simply because Jim Carry is in it and hasn't been in films for years. One big benefit the Sonic movie has going for it is Jim Carry and he decided to be in this movie after a multiple year hiatus. It also helps he delivers a performance very much like his earlier zanier work. This isn't helping the movie do better in the box office, but I'll also add that the human characters in the Sonic movie are much, much better than the human characters in Detective Pikachu.
-As many are pointing out, the delay to February was a smart move because the Sonic movie is competing with very little else for the next few weeks.
-I think the Sonic movie had better marketing. Between the actual commercial advertising budget, and the film did manage to generate buzz and trend on Twitter and such multiple times due to the design shenanigans which even ultimately turned into positive buzz even if it was negative at the start. I know this is a weird barometer to use, but the controversy lead to things like talk shows talking about the Sonic movie, when Detective Pikachu didn't have the same benefit.
Now it is to be seen how the movies legs work and how it does domestically. I do think the Sonic movie is set to perform better than Detective Pikachu in the states and the West, but I also don't think the Sonic IP is as big as it is in China or the like. Really it's going to be up to how the movie does domestically eventually to if it'll gross more than Detective Pikachu or not.