declare
  l_stmt long := 'c1 int';
begin
  for i in 2 .. 999 loop
    l_stmt := l_stmt || ', c' || i || 
      case mod ( i, 3 ) 
        when 0 then ' int'
        when 1 then ' varchar2(100)'
        when 2 then ' date'
      end ;
  end loop;

  execute immediate 'create table t1 ( x int, ' || l_stmt || ')';
  execute immediate 'create table t2 ( ' || l_stmt || ', x int )';
end;
/

insert into t1 (x) select object_id from all_objects;

insert into t2 (x) select x from t1;
commit;

select segment_name, bytes from user_segments
where  segment_name in ( 'T1', 'T2' );

-- results from 19c
SEGMENT_NAME   BYTES      
T1                   917504 
T2                 88080384 

-- results from 11.2
SEGMENT_NAME   BYTES       
T1                   2097152 
T2                 109051904