ls 50 metas compared to floorstanding speakers

They are far better in the nearfield. They are designed to sum their acoustical output right at the output location, versus closer to 3 meters for a 3-way speaker. In that use case, they are leagues better than a traditional 3 way vertical array (not including 3 way point source designs like the Genelec 8341 which would be better). Not to mention you could stand above and below the LS50 Metas and would still have the same output because of the uniform vertical dispersion, whereas a 3-way dome and cone speaker wouldn’t sound very good if you stood above the tweeter axis. The Focal wouldn’t even compete here.

In a large room if your listening distance is greater than 10 feet, the bigger, multi-driver speaker has a major advantage in power handling and dynamics.

Really depends on your use case.

are bookshelf speakers generally better for nearfield listening than 3 way speakers? what is the "boundary" between nearfield vs. not?

3-ways are perfectly fine for the nearfield in a coaxial arrangement. In a vertical array with offset drivers typically manufacturers suggest >3m listening distance for a 3-way.