First of all, both phrases are correct:
- pitted against; pitting against; pits against. : to cause (someone or something) to fight or compete against (another person or thing)
- Most in this case is used to emphasize formidable; it's more poetic and not as common in everyday use as very, but still correct.
As for the period, it's just a single sentence in the tier description, not a lengthy text or a multi-bullet list. I hardly think a lack of a period is worth freaking out for.
Second, even if they were not correct, that is your biggest concern? So many bugs and tuning issues that make the game a miserable experience, and you're more concerned about proper grammar. I myself studied English for five years in university (BA and MA), so I'm very passionate about linguistics. But even I'm not that big of a fanatic. I'm almost afraid to imagine how you react any time you see younger people casually texting each other.