'"1000s of terminals" sounds scary, but it really doesn't matter. Small teams can build robust complex systems.'
Nobody of any competence in the subject would dispute that.
'Maintenance and updates are a separate thing.'
Utter nonsense, because in the real world it is a continuous program of installation, maintenance and update and that is what the big users are aware of and want. They have a business to run, are not stupid and understand that it all can't be magically installed in an instant without impacting their day to day operations. I guarantee you that the hardware / firmware levels of even dumb terminal No 1 and dumb terminal No 1000 will differ due to changing component availability during manufacture . If your terminal has any kind of OS I bet there will be revision differences there to.
'If systems required to have good documentation and interoperability, there wouldn't be a need for a single big company to service them.'
Again, drivel. PC's, networks and widely documented and interoperable OS components have been available since the Nineties and still there is a vast industry nailing them all together and struggling to keep it all working. If it's interoperability of the application you want, then the question is 'what do you want it to work with?' when that question is answered then the reality is that if it wasn't in the specification the next statement is 'I am sure we can, it will cost you this'. No business is prescient or a charity.
'This is another fallacy. In corrupt system of course the tenders will be structured in such a way that only the big players could realistically participate.'
This is where you finally display your tin foil hat.
You do understand that the customer sets the terms of the tender don't you? So if they set the terms such that only a large organisation can provide a feasible solution to meet their needs then that is their prerogative? Again, in the real world, it's someone doing their best not to get sacked for committing large amounts of their companies finances to some outfit with an unknown track record and unproven resources.
It's not corruption, it's something far simpler, it's human nature that when you don't really know what you are doing or are not interested in the technicalities or just have too many issues on your plate, you play it safe.
The old adage 'No one gets sacked for buying IBM' is as true now as it was when it was coined.