Dunsparce is in no way High tier. I'm training one now and it's all right, but certainly not hitting hard enough/fast enough for a high tier mon. Even max Power Return + Silk Scarf doesn't OHKO a lot of things.
I've got everyone to about Lv 40 now (Solrock DW, Dunsparce, Sunflora, Emboar, Azumarill and Crobat). And can honestly say none of them are high tier!
I'm on a mission to train every Pokemon Family during a playthrough of 3rd to 5th Gen! Currently at: 532/602!
Current Team (White 2 [4 badges]): Vulpix/Zoroark/Mr Mime/Cherrim/Deerling/Marshtomp
Current Team (Black 2): Solrock/Emboar/Sunflora/Crobat/Dunsparce/Azumarill