Change your job, or change your job. You could discuss how the lack of documentation is causing the team issues; maybe even frame it in a way to highlight how

Change your job, or change your job. You could discuss how the lack of documentation is causing the team issues; maybe even frame it in a way to highlight how documentation will make him more useful (more time to spend on architecture vs answering questions, better chance that his architecture will be implemented as designed). Express your concerns about introducing new technologies -- something that I've had some success with is asking 'which library/framework/dependency will we able to remove if we add this new one?'. Propose that the architect allocate time to training the team or being on pager duty or fixing maintenance bugs if they feel strongly that a new tech is the best decision. If that doesn't work and the situation is unworkable, then consider a move.