The anime did have a pretty strong continuity up until the end of DP. It's why the OS, AG and DP all felt like one long continuous series. Each saga flowed into the next, old characters returned, Ash still used older pokemon, and they referenced things from past episodes. It wasn't until BW started where they came up with their semi-reboots every saga. The tail-end of BW had returns of Dawn and Charizard, but again that seems to have been a one time thing. Both XY and SM are also rather standalone sagas from everything else. Oddly enough I think it was Brock also leaving that made every saga feel like a reboot. Without one returning companion around every saga feels like it's own thing. As much as I didn't like DP-era Brock, it is especially noticeable once he was axed each saga feels like its own thing.