I agree regarding the TPCi dub. I too feel something really bad happened to the English dub in DP. I actually thought TPCi did a decent job with BF (minus Ash and Max- god damn, Veronica Taylor and Amy Birnbaum needed to come back ASAP). I still personally preferred 4Kids at the time, but I felt TPCi was decent at the time.
On the other hand, like what you said, DP was horribly dubbed in my eyes. At least the first half, anyway. Ash and Brock sounded constipated and like they were smoking some vicious cigarettes, Team Rocket wouldn't stop the alliterations, assonance, etc. Add all of that together, and it created a disaster.
BW marked a spike in the voice acting, and everyone but Zoppi got at least tolerable to good. Same here. Still, it just isn't the same, like what BW116 (the flashback episode) made clear in my eyes.
Holistically, 4Kids did the better English dub in my eyes. Gotta say, I'll always miss them for Pokemon.