>>56059803depends if you can pull it off or not.
keep in mind those regions only have 3-4 gyms that can be completed in free sequence. and Johto is notorious for having poor level scaling.
so just be careful, it's a hard thing to nail down. if there's big gaps in the levels you will just be encouraged to face them in order anyway, and if they're too close in level that whole stretch of the game will feel stagnant. sometimes a more structured approach is appropriate.
unless you plan to use level scaling, which is a whole other conversation.