In MC6 case its true that by utilizing enough vitamins and DS disk, you'll be able to kill most of the mobs possible hence maximising your loot. But with boss card you can barely finish them in around 3 minutes time per card by using cheaper alternatives (for example using ultimate or champion form, in my case I can solo the MC 5 bosses with only my Monodramon and MC 6 bosses with Kyubimon). Going all out with skill-breaks and final form of your particular digimon will kill it way too fast at the cost of your ds consumption. On the other hand, you would get the same outcome with a cheaper alternative if you're not maximising your damage. No matter how cheap vitamins and disks considering your current wealth, everyone would want to maximise their loot, in this case if you are getting the same loot but with higher running cost (vitamins, disks, chicken combos) than it should be, you are not maximising your loot after all.
Sometimes people may appear "cheap" but actually they're just playing "smart", give it some thought