Yes he's wrong: to be promoted you must be doing the next job already and the management must be terrified you leave.
Sure about this?
This isn't even possible everywhere - doing the next job, for example, isn't generally possible for lower wage jobs. How the heck are you going to train for a shift manager position by learning the job when you literally don't have the authority access to do it?
You don't.
Terrified that you leave? Try that in a call center. You, no matter how good you are, will be easily replaced with another warm body or two and folks quit these jobs all the time.
Are you sure petulantly slacking off won't make one happy? I mean, what if you get joy out of seeing how far you can push that button - or alternatively, don't get satisfaction from a 'job well done' like you are told that you should? Or maybe you only do well for some recognition that you aren't getting... or maybe jobs don't give you satisfaction at all. They merely give you the means to do stuff that does make you happy.
The context here is software development. Depending on what field you are in, I would tend to agree with you that it might either not be possible or a bit harder.
That said, even in software, you don't always 'have the authority' to do that other job. But does that matter?
Example: you're the junior, new to the team. When the team does backlog maintenance, everyone just slaps some estimate onto the barely defined ticket and calls it a day. Sprints slip all the time because tickets "explode" once you actually start working on them. The team lead does nothing about it, the PO couldn't care less, he just screams at everyone when none of the tickets are done at the end of the sprint.
The junior could just resign himself and play along. Or he can start asking "dumb questions" during backlog maintenance. I.e. start a proper discussion. Suggest tickets to be split etc. The bad team lead and PO might ignore this and even actively try to get back to just slapping on estimates, not actually do the splitting or say "yeah I'll do the splitting by the time we do sprint planning" and then obviously nothing ever happens.
Do it yourself! Offer helping out, to give them a chance to be part of it. They might refuse or try to "pull rank". Ignore them. Split the tickets. If you can't do it before a sprint starts (e.g. cause they'll notice and try to pull rank), split them after you've started on one of those bad tickets. Split it into 3 nicely sized ones and at the end of the sprint you can show that hey, ticket 1 is finished, ticket 2 is almost done and ticket 3 isn't even started yet. We can release the functionality of ticket 1 to customers even!
You've just done all of the following:
Shown that you're not the junior you've been hired as but much more!
Ignored the team lead's authority when it became clear that even when shown the proper way, he's not going to act
Ignored the PO's authority when it became clear that even when shown the proper way, he's not going to act
Let's take this to the call center:
Folks quit these all the time, like you said. Even the shift leaders or managers. I don't know enough about call center operations to know what the equivalent tasks of the little story above are but I do know from experience w/ some of our guys that it's totally possible there as well. We had a really great QA that came in through the call center. Started as a regular rep, became a shift lead, moved into QA and then became a BA. He was awesome at that. Knew everything by heart or was able to quickly try it out in-product. Heck the department lead came in through the call center as well. Similar trajectory but didn't move over to the software side and stayed on the business side.
It's not about petulance, it's about motivation. I'm in a similar position to the author but acting more like you would want; I care about being good at my job and want to deliver because that is how I was raised, but there is a constant tension in me that this is the "wrong" approach since no company actually rewards loyalty or expertise, at least not nearly as much as self-promotion and being a corporate mouthpiece.
Regarding promotion and being indispensable, that cuts both ways - in some roles being impossible to replace also means you are impossible to promote, since the next step up the rigidly defined corporate ladder may not have sufficient overlap with your current role.
You can love your job and hop out sometimes. But petulantly slacking off like OP says, is not going to make you happy.