Access issue for system queries

Dear all,

I have granted access to pg_read_all_stats and pg_read_allsettings to
user..still they are not able to receive results from this query.its
empty..we can run SELECT * FROM pg_stat_statements alone..but not below
statement..what could be the reason?

WITH statements AS (
SELECT * FROM pg_stat_statements pss
JOIN pg_roles pr ON (userid=oid)
WHERE rolname = current_user
)
SELECT calls,
min_exec_time,
max_exec_time,
mean_exec_time,
stddev_exec_time,
(stddev_exec_time/mean_exec_time) AS coeff_of_variance,
query
FROM statements
WHERE calls > 500
AND shared_blks_hit > 0
ORDER BY mean_exec_time DESC
LIMIT 10

Regards,
Arun