As I Explained in the summary, most of the tags for the monster spawner doesn't work. Like Delay, MinSpawnDelay, MaxSpawnDelay, SpawnRange, SpawnCount, MaxNearbyEntities & RequiredPlayerRange.
What I thought it would do:
Just as the wiki said these tags would do, like shorten delay, Causing it spawn again & again in quick succession.
What really happened:
Nothing, It wouldn't even spawn anything.
How to reproduce:
Put in this command:
setblock ~ ~ ~ mob_spawner 1 replace