After migrating taskwarrior to 3.0.2, running the ready report took:

253 tasks, truncated to 35 lines

real	0m0.562s
user	0m0.401s
sys	0m0.148s

The same tasks and reports in version2

253 tasks, truncated to 35 lines

real	0m0.248s
user	0m0.145s
sys	0m0.095s

I noticed that the sqlite storage uses JSON instead of regular columns for some attributes. This is likely slower than a sequencial read of a file with the same content.