fastboot seems to work, can transfer files but doesn't actually flash or boot images
You can't root with ADB or Fastboot because you don't have the ''adress" where the files will be sent. Mediatek devices need a map file, called scatter files which maps the memory and tells the flashing tool where every file should go, the start adress and the file size.

As they run Android,  Mediatek devices can be  manipulated with adb and  fastboot (depending on manufacturer: Alcatel and Huawei seem to support fastboot commands).

META mode is like fastboot, as you've pointed out. Besides you can enable ADB in META mode, it is used by hacking tools to access internal memory, as an example for network unlocking, IMEI repairing and so, you need special drivers CDC and VCOM to get it work though.