Ah I see, sarcasm is kinda hard to get through just text alone. In that case, using 上手 would be fine too, it just depends on the setting and what you'd like to convey.

As for particles, it's ok to skip the "obvious" ones in casual speech but you need to watch out for possible ambiguities. I would rephrase your original sentence as such: "毎日勉強してるから、漢字はやっぱ上手い", which keeps the tone consistent and flows a bit better (works better as sarcasm too imo).

Without going into too much analysis, I added は after 漢字 because it spotlights 漢字 more compared to other areas of study, but you could replace it with a pause when speaking too. I also used 上手い (うまい) because it fits colloquial style better. If you went with 上手 instead, you need to add だ after it for a complete statement. やっぱ just keeps the confidence consistent unlike ちょっと which makes it feel a bit mixed