Of course, newbies can divide their proportions however the fuck they like. It does not have to be equal. There is personal choice involved, especially when "discretionary" is already in the name. Look up the word "discretionary." It means having the ability to choose and to use one's own judgement.
I think that many times the 1/3 in each category is mentioned as an easy way for a newbie to decide how much to put into each category, yet in the end each person is likely way better off if they use their own actual brain (if they have one?) to pick amounts of their discretionary funds that are comfortable for their personal and specific situation and also allows them to not end up overdoing their allocation in one category or another.
Exactly, The essence of person starting their investments with common sense is so that they can be able to use it for their own personal judgement rather than copying someone strategy that may not later work for the person.
It is a discretionary income, so hell yeah, person can decide how they can divided it in a more comfortable way. If they want to put 50% in buying and 30% for consumption and 20$ in reserve, that's the person call. If another person want to do something different too, that is also the business business too. They should just do what ever suit their ability.