In essence, it depends on the audience and what they are looking for.
Walkthroughs are dependent on viewers seeking information on the particular game you're creating this content for. The problem is if the game is searched or not. A game like Assassin's Creed Valhalla will likely have a high search due to being a new, highly anticipated game. But a game like, say, Star Trek Armada II might not get that much traction because it's old and not as popular at the moment. So it will depend on what games you wanna make the walkthroughs for as to whether viewers look for them or not. It's easier to make walkthroughs because it's considered an evergreen video that can still be searchable years later.
Gameplay videos are dependent on the gamer themselves. If you do commentary viewers look for the gamer to be entertaining enough. Dr Disrepect was a character with a crazy personality that made people laugh, Wacky Jacky is like a teacher who's constantly teaching people how to play. If you're not commenting gameplay depends on what type of gameplay. You're either an amazing player or you use your lacking skills as comedy. Gameplay videos are much harder to manage because it's dependent on the player themselves to make the gameplay worth watching.
So in essence it depends on what you're looking for on your channel. Are you looking for views or are you looking to be the face of your channel?
Videos that help people often get more SEO with google and the algorithm. Most people watch a video for help, and therefore, will watch the video longer.
As a person that makes tutorials, i can confirm they get a lot more views then gameplays. They can also get in "suggested clips" in google, which is good for views.
To my experience the competition is usually harder for let's plays than for guides/tutorials. At least for the games I have been creating content there are hundreds if not thousands for channels doing let's plays with a much smaller amount of channels doing guides/tutorials. As a smaller channel it's always been hard for me to compete with larger more popular channels so my tutorials/guides usually do much better than my let's plays. I see the guides/tutorials as a gateway for people to find my channel and then hopefully some of the viewers finds their way over to my let's plays for that same game.
Walkthroughs - these tend to have information on how to beat the game, and other important stuff, especially for Story-based games.
Gameplays - tend to be casual, fun, informative, or a combination of all three.
I would say walkthroughs are better than gampleay videos mainly because it is easier to be engaging and find things to talk about in the video, especially if you are experienced at the game.
However, if you have an engaging or relatable personality then it might be easier for you to make gameplay videos!
You know, my gut tells me a walkthough is better than a general gameplay video. If you can do a walkthough of a difficult level, that could be helpful for some people LOOKING for a walkthough of a difficult level. In the 90's all we had was magazines to read walkthroughs, and sometimes text guides. Video walkthroughs have helped me a lot in the past, especially on BioShock.
So it might not have fast view potential, but it can definitely have long term evergreen potential. People still play unpopular games. Like, Half Life 1 is SUPER old now, but people still play it sometimes, and those people still might get lost on a level. So I see nothing wrong with a walkthrough. Though simply watching someone playing a game for the sake of playing has limited watch replayability.