Interesting adaptation to the new mechanics; I expect the rates will be significantly lower, but that may not mean much as it seems likely to produce 'enough'.
Y-level references in the tutorial would have been helpful [I'm guessing you have the magma blocks at Y= ~28 and the enchanting tables at Y= ~12].
A few questions and observations:
In the water flumes between the raised magma block runs, why not use the two sign with elevated water source block design to avoid teh gaps in the water flow?
Why not place the magma blocks @ Y=37?
This gives greater drop height and / or more space to fit a stroage system under the farm.
Granted there would be some water removal needed between the pillars, but the amount is comparatively small and the gravel (left for last) could be cleared from beneath as needed.
I'm also not convinced the final step (removing the monument structure under fire from the guardians) might not be as difficult (if far less repetitive/fiddly) than draining the monument.
Assuming guardians will spawn in the bubble columns [not mentioned in the video and unknown to me at present], using bubble columns to drop the guardian out of the spawner might be preferrable to the redstone blocks substituted for the glass in gnembon type designs after 1.12.
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.