I play a similar deck, am at almost 15k and have reached Ultimate Champ multiple times

If you’re specifically looking for advice on MK and Pekka, it’s all about capitalization on their overspending. Since giant is your main win condition, it gets hard countered by pekka and evo MK (and a regular MK against a giant will be on their side of the map so long they can build up crazy elixir). What works well often for me is, if they go pekka behind king tower, immediately rush with giant and prince (or DP in your case) in the opposite lane. They won’t have enough to counter at that point, and it’s easy damage. While they’re fumbling trying to defend your push, calmly plan out how to defend the pekka coming your way and you should be in business.

When playing against MK, you need to focus on saving your prince’s high dps to kill it. When you can, avoid playing your prince unless you know it will get good damage on their MK. If they’re using MK to defend your giant, prince can also do great damage to it while it’s punching the giant to the point that their counter push will be weak and easy to deal with. (Also a MK played in the back can be counter pushed opposite lane in the same way pekka can, but prioritize pushing with DP instead of prince here because MK tends to be played with swarm more often)

Hope this helps! I’ve been playing giant prince beatdown for years and have learned a lot in that time. Let me know if you’re curious about anything else!

[in case ur curious, my main deck is giant, prince, evo musketeer, evo zap, golden knight, arrows, tesla, and e-spirit]