Back in MY day...
I'm kind of in the same mindset!
I've done plenty of runs with both Torterra and Infernape (even both) and I'm 100% commited to using Empoleon this time.
When I think of it, using a Fire-type cheapens the game a lot in Sinnoh. A few days ago, a Youtuber (Flygon something) finished a Diamond Nuzlocke with JUST Fire-types. Diamond. So just Infernape and Rapidash.
Why are you picking Infernape with the DP-dex and subsequently picking Rapidash if the Dpt-dex? I mean if you don't mind running the horse even when you have far more options (Flareon, Houndoom, Magmortar, HeatRotom), why not use it when the Dex is more limited (DP) and free-up your starter choice?
Also, I see you are doubting on a Grass-type and end up picking up Carnivine, but you already have a Grass-type in Abomasnow? Similarly, in the Dpt-team you have Rapidash ánd Magmortar?
Empoleon, Lopunny, Togekiss, Skuntank, Carnivine and Froslass.
So I definitely wasn't properly caffeinated when I made that post and just realized how messy that was. I'd probably sub Infernape for the horse in that case, but then I'd be eliminating Floatzel in favor of Empoleon. OR I could just pick the penguin and choose to complete the run without it? Not for nothing but I can't remember a time where I decided to ditch my starter, but that may be an option if I don't care enough? As far as the platinum dex, I'd eliminate Rapidash and consider Drapion, Toxicroak, or Abomasnow whereas they're 3 of the handful of Sinnoh pokemon that I've never actually used in a playthrough.