If you have the hours, the much easier route is to get a command elsewhere and then apply as a DEC. That is a lot easier to do than the internal upgrade process which can take quite a few years and is ultimately in key moments completely dependent on the likes, dislikes and sometimes flawed understanding of company procedures. Especially the base captain, who does not need to be a trainer, has a very important role to play, without any real oversight at all, basically, he determines the fate of every first officer and is the ultimate power in his base.