Overall a decent idea.
The difference is that the latter is much more powerful and almost forces you to specialize: If Fire skills cost 1 to 5, and I have a -3 memory cost, then I can equip all fire skills at an average of half cost. This could easily be 20+ memory saved, for a few skill points invested. On the other hand, if that same investment gives you +5 fire memory slots, you still benefit by having a free fire spell or two, but not to the same extent.
This definitely depends entirely on the scale and balance though.
In my rough, base example, if Master skills cost 10, you would need 18 Skill School points devoted to bring that down to 1 cost.
To bring the Adept 5 Memory point skills down to 1 Memory, you would need 8 Skill School points invested. If the base cost of Adept was kept the same proportionally as live, it would actually cost 6 Memory (since its currently 3 Slots in game), and would thus need 10 points invested in a Skill School to be reduced to 1 cost, which actually upon review sounds like a much nicer number in general and keeps things standard with the current in game values. Investing 10 points in a Skill is quite a heavy investment.
The numbers clearly depend on many factors, such as "How many Skill Points can we get total?" and "What values work best to incentives specialization without squashing hybridization and generalization?"
Also, there would need to be a decison of "If a player goes all in on a singular Skill School, is it fair and balanced to simply let them memorize that entire School's worth of abilities on one bar, since they have specialized so deeply?"
My personal opinion is "yes" to the above. If you are limiting yourself to strictly "one" main Skill School and throw so much of your character's potential into it, I don't think the system should deny you the ability to slot all of your skill's abilities, considering you are now "master" level in the game's lore of that specific skill.
To me, this is like the difference between a "true pyromancer who knows each of his abilities by heart" and an archmage who "knows many fire spells along with his whole lexicon of potential spells, but must focus on keeping them learned alongside his other tools, and must select the right tools."
To me this just feels to reflect the actual reality of how memory and specialization works in the real world.
Someone who is a specialist in a given field can readily recall specific field related information very quickly and easily because they are familiar with it at an intimate level, while a generalist (think general practitioner medical doctor) knows a large amount of information about a wide subject area, but many times will have to consult additional materials to help make a more specific diagnosis or will have to refer you to a specialist in that specific area of medicine.
The specialist has that information on hand mentally and due to their experience, while the generalist has the information available through their ability to index and search for the information or to connect to someone who knows the information.