Mysql – Does latin1 have performance benefits over utf8

I have a table in utf8 with > 80M records and one of the columns (char(6) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL) can contain just latin symbols ([a-zA-Z0-9]). Does it have the sense to convert this column into latin1?

MySQL doc says:

To save space with UTF-8, use VARCHAR instead of CHAR. Otherwise, MySQL must reserve three bytes for each character in a CHAR CHARACTER SET utf8 column because that is the maximum possible character length. For example, MySQL must reserve 30 bytes for a CHAR(10) CHARACTER SET utf8 column.

I made a test – created 2 tables with the same 50M records:

CREATE TABLE `t_utf8` (
  `c_1` char(6) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
  UNIQUE KEY `index_t_utf8_on_c_1` (`c_1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=COMPACT;

CREATE TABLE `t_lat` (
  `c_1` char(6) CHARACTER SET latin1 COLLATE latin1_bin NOT NULL,
  UNIQUE KEY `index_t_lat_on_c_1` (`c_1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=COMPACT;

but MySQL says that they have almost the same size:

           Name: t_lat
         Engine: InnoDB
        Version: 10
     Row_format: Compact
           Rows: 57557700
 Avg_row_length: 30
    Data_length: 1741668352
Max_data_length: 0
   Index_length: 0
      Data_free: 2097152
 Auto_increment: NULL
      Collation: utf8_general_ci
 Create_options: row_format=COMPACT

           Name: t_utf8
         Engine: InnoDB
        Version: 10
     Row_format: Compact
           Rows: 57554528
 Avg_row_length: 31
    Data_length: 1810874368
Max_data_length: 0
   Index_length: 0
      Data_free: 3145728
 Auto_increment: NULL
      Collation: utf8_general_ci
 Create_options: row_format=COMPACT

Why does it so?

• MySQL 5.7
• InnoDB

P.S: I made the same test with MyISAM and got expected benefit: table with latin1 – 383Mb, utf8 – 1Gb. But why it does not work for InnoDB?