It did not, actually, to clarify just this one point: there was a decrease from Season 12 keeping 47% down to 38.3%, then they shot up to 92% in S14, and then back down like you said to 36% in S15. TPCi's first 1/xx dub episode is actually in Season 13, in fact, DP186 (there's also the random 100% OST kept in Ash vs. Tobias to compensate but you get the point).
DP actually has a weird trend in the dub: it starts out with Season 10 keeping 34.3% of the Japanese music, then in the middle "peaks" with 45-47%, and then goes back down in Season 13 to keeping 38.3% of the Japanese music on average. It wasn't a consistent upward trend at all, unless you exclude Sinnoh League Victors, a lot of people seem to be mistaken about this.
The dub change was done to cut costs on said budget, and save money: TAJ at the time outbid 4Kids for a cheaper rate to produce the dub, TPCi saw they could save cash on production by doing that, so that's what happened. Hence, we saw the departure of all of the original English voice actors and writers with the exceptions of James Cathcart & Kayzie Rogers. What's even weirder is TAJ kept using stock 4Kids dub BGM every even numbered episode for the 2 seasons they dubbed on their own (BF & DP Season 10), as well.
Nor does it do anything about all the rewrites they made to Ash & Cross' dialogue like "Might makes right," "Kay," and Ash's slang-y dialogue either, or the questionable voice acting quality.
Ed Goldfarb isn't the direct problem in terms of music replacing: Akhil Gopal and Dave McNair do the actual music mastering and editing for the dub, so they deserve the flak for doing that- Goldfarb's at fault for spamming the same 4 themes in almost every dub episode, especially his Batman theme over 110 times in 60 episodes (which is the most spammed a dub music piece has ever been in the 21 years the dub has been on air) and not composing fitting pieces for the mood in certain scenarios (such as playing circus like music in Totem Battles). Ultimately, Kenji Okubo as Kevin said orders all of these things among DuArt ordering OLM via TPCi to make visual edits for the dub, so he bears the bulk of the blame for it all.
Where did you get these percentages? Are these represent time on music or just number of soundtacks?
(a) From a document online that essentially lists how much percent of Japanese music was kept in each season, Movie, etc. in the English dub of Pokemon (for the main Series)- if you want, I can link it.
While it's a decent enough theory, I think TPCi is just replacing most of the OST to make royalties as per standards of practice with the dub over the years (or rather, DuArt is in the main Anime dub and associated films): I mean, they can leave the OST alone for Pokemon Origins & Generations (though the latter is a questionable dub VA & script wise imo, but that's irrelevant) so there's no need to replace it here.
