my last guide is out of date so here's how I think they're doing it currently and how to disable it

go to Documents\My Games\Binding of Isaac Afterbirth+ Mods\revelations_1536643474\lua\revelcommon\bosses

find this line: function REVEL.ModifyBossHP(npc, position, force)

delete everything indented under it but don't delete the associated "end" that closes out the function

in between the function definition and the end insert the line "return npc.MaxHitPoints"

(they probably set the base hp of the bosses lower to compensate for the hp scaling so you can experiment with the value you return, for example you could do "return npc.MaxHitPoints * 2" to instead to double the hp of all revelations bosses, although double is probably too much, experiment and report back a value to multiply by that you think is fair!)

I tested it with very high dps and very low dps and with this change the scaling is all gone!