pt-variable-advisor sort_buffer_size-1 says to leave at default when it's already the default (MySQL >= 5.6.4)
The default value for sort_buffer_size changed from 2097144 in versions before 5.6.4 to 262144 in 5.6.4 and higher (see https:/
The current sort_buffer_size-1 check is hard coded to fail if sort_buffer_size != 2097144. When the check fails it shows a warning saying the variable should be left at the default value, even if it's already at the default 262144 in 5.6.4 and up.
This should be updated to perhaps check the version of MySQL and adjust the expected value accordingly, or to specify that sort_buffer_size should be set to 2097144, or updated so it's more relevant in the latest MySQL releases.