Actually, a very good question.
Grid 2019 is a very good game, but miss some personality. It is just grinding through the events for cosmetics.
Comparing to the pervious title, Grid Legends has something better, something worse.
For example, car handling in Legends feels better. They returned drift - very good drift. Eliminator races are great. Multiclass races are great. Story mode finally offers something different.
At the same time, lots of minor bugs that should have never made it into release. Awful replay camera, that ruins all the beauty of the game. Very discussable gameplay solutions, like Electric boost, Lap boost, CarNage derby, Stadium Trucks with ramps, Endurance races (duplicate of multiclass) without weather, day/night change and pit stops.
Again, story mode, though the story itself is good, sometimes feels very detached from the races you actually drive. There are some very good moves like Yume crash, or young McKane stealing his uncle's car and wins actual race with it. But that is it. The rest is just grinding through the grid again.
It looks like these were supposed to be one game, that was somehow teared up due to some business issues. Grid 2019 was rushed into release sooner and was very raw, and new team working on Grid Legends somehow didn't succeed at the level we were expecting them.
Which game has more replayability? Eh... I would say I prefer to return to DirtRally 2.0 and none of the latest GRIDs.