Planetside 2 has them on on huge map, but as soon as more player are nearer in one area the system got problems too. Lags, Jumps and wrong running clocks (different speeds an the map). They shard within a server. But PS2 Networking is really good and optimized, better as most current games, and Planetside 1 + 2 (and parts of the Engine) are 20 years old. Most new games are overwhelmed with 64 Players. PS2 can handle 200 on small areas without any problem.

UO Outlands (by far the most active current UO free shard) hovers around 2500-3000 characters online nightly (1500-1800 unique IPs).

Shards in UO are called that way because of the lore (gem shattered into shards), and each shard is just a regional server completely isolated from other shards. So they are not very different from Minecraft or Planetside servers. Sharding in other games split the user base based on active load. This is not the case with UO.