I put 100 hours into Scarlet since release, never saw a single shiny. Even with shiny charm, sandwiches, Masuda, still never saw one.
Last week I finally got a shiny Snorunt. Five days later I got another shiny Snorunt. On Sunday I got three shinies in a day - Rookiedee, Ekans, and Noibat - and I only used a sandwich on one of them. The other shinies were all random overworld encounters while I was doing other things.
I legit didn't even see the shiny Ekans because it's green and blended into the grass. I actually thought it was a rendering issue where I ran into an invisible encounter because of how slow and laggy the game is.
Really enjoyed the DLC. Ogerpon is adorable, Carmine and Kieran are interesting characters, there's at least some semblance of a story. I liked it. Didn't love the design of the Loyal Three, but it makes sense in context of the storypokedex. I wish the new pokedex had a few more returning pokemon but the ones they brought back were all good choices.