I believe the main games continue being button smashing...
It is turn based because it is a spin off RPG based in the franchise.
After the success the spin-off will probably receive sequels... it is not the first time the spin off become more popular than the main games (Persona, NiER, etc).
Yakuza Like a Dragon is not a spin-off, its the next main game in the series. In Japan the game is called
Ryū ga Gotoku 7 . They just changed the name in the west to make it clear its a new saga staring a new main character.
A spinoff, is Judgment and that one has the same action combat as other Yakuzas.
The reason this game has turn based combat was because they did an april fools video where the game had turn based combat, and the reception to the video was great and made alot of ppl excited to have a new yakuza with turned based combat. They decided to keep developing the turn based combat for the new saga, but they told if the games reception to the combat was bad they had no problems in going back to action combat again. The game mechanics seems to have been well received so i doubt they go back to action combat for the next one.
With some many games abandoning good turn based combat to implement mediocre button mashin action combat, im glad this one did the oposite. I love all Yakuza games, but i welcome the new combat mechanics. My Favorite JRPGs are all turn based. (FF7, Persona, Dragon Quests).