I mean the in depth possibilities to edit gameplay is imo ways better than in FIFA17-19! I don´t speak from the base / default gameplay of 17 or 18. There was a huge change in the basic programmed Gameplay by EA since FIFA 20 which we all easily recognized. Just a basketball match after another I remember. Playing 2x8 or 2 x10 minutes in default FIFA 20 was like Chicago Bulls vs NY Nets. If we could access the same areas in FIFA 17-19 I am 100% sure the gameplay with the default base of these older FIFA´s would let you forget FC 25 in minutes. So, yeah it remains only the locale.ini or the iniTFS edit for 17-19. But there is a section in Frosty Editor where you can view the "gameplayattribdb" a.e. This gameplay related section is not accessable via Editor. Like Topaz said you can open it in HEX editor when you know what are doing and you can make edits to the gameplay in FIFA 18 a.e. Fidel Gameplay released back in 2018 an modified Version of those gameplay related but hardcoded by EA files in his mod called FAES AGPE gameplay. He hex edited the gameplayattribdb, as well as the "Neuralnet" section. Idk if you ever tested this FIFA 18 mod?! But I may remember
@Topaz knows the old Fidel mod.
So just from the possibilities I see much more in depth by editing ebx files than the locale.ini in FIFA 17-19. ANd I know many many Gameplay Modder don´t trust the locale.ini modding to have an effect on the Gameplay because of it´s just putting strings in a ini. Anyway, that´s another topic how effective is locale.ini modding by reading out the game exe. Fo me personally it is effective but like yourself writing not sure what exactly working in the locale.ini. With ebx modding you have an safer way to recognize what´s working on the pitch.
The point you stated what the output is by ebx modding is standing for me on another paper. To find a balance with aaaaall those ebx files is a art for hisself of course. Many gameplay mods are feeling still broken, but not every modder have the same skills to understand what file needs to take care when editing another ebx file and causing another strange behaviour. And finally I am not very faithful to have let´s say in 10 years from today a Gameplay base like the early Frostbite Games again. So it´s good we can use Frosty editor and entering the ebx file structur imo.