To be frank, SSJ4 doesn't really have a set multiplier either. It seems to just continually grant more strength the more Ki you have or more control you have. We're explicitly told that the SSJ4 you see most of the time is actually nerfed, because Goku isn't at Full Power, which results in him not performing as well as he should. This is very clearly established with his fight with Baby--The massive jumps in power I listed are the amps it gave a Goku on death's door. Once he gained his full power, he was able to just wallop Baby, and he can continually absorb Ki to grow in strength further, like he did to the Revenge Death Ball. This is really consistent, because when Goku fought Nuova he didn't even really have the Ki to transform at all, and was just forcing his body to do so, and he was fighting comparably, whereas when Goku fought Omega, after getting Ki given to him for his "Super Full Power" he utterly dwarfed everyone else and was directly stated to be so close to Omega the difference in their powers was impossible to tell.
So you could really say that SSJ4 is like, the perfect form? It has basically no drain, can create massive stores of power out of nothing, can sap power to fight above your weight class (making it have a lite version of the unbounded multiplier UE and UI have) and operates as a potential unlock that puts you in your prime body, meaning your prior physical circumstances don't really matter. While SSJ4 within the context of it's story won't naturally give you a SSBKK, SSBE, or UI/UE buff, you can work your way there pretty cleanly via just Super 17'ing your way up the ladder. The difference is that SSJ4 focuses on bettering the fundamentals, like precision, senses, stamina cost, improving the prior forms, etc. whereas UI and UE come with hax.