What applicants sometimes do is provide some aspects of what they want their recommenders to talk about - e.g. provide a write up that recommender does not copy/paste from but rather providing guidance and examples that the boss then can choose from. Supervisors often are busy, forgetful, manage many people and may not remember the best example at the right time, esp if you had a recent misstep. You could give them a list of your accomplishments, achievements, examples of certain aspects.
P.S. At the end, unfortunately a number of bosses still refuse to write the recommendation letter. Not always out of laziness but sometimes if they have not gone to business school and never had to write one, they are concerned they will screw it up or frankly don't want to learn something new they don't need to, so maybe a little lazy. Anyway, then it is up to the applicant to choose what to do. The AdCom knows that this happens in certain countries more than others and chooses how much they want to value/weigh the LOR's accordingly.
Good luck to you MCTTW in this journey! Hope your boss turns his story around.