A REAL yirei shomayim pays attention to his own kavanah, and doesn’t worry about what others are wearing. Who are you to decide who is a yirei shomayim based on footwear? I know several people who are true yirei shomayim that don’t wear hats or jackets (with the exception of the shabbos suit) – not because it is inconvenient or uncomfortable for them, but rather because it is what they grew up doing, and have always done.
Do you think HKBH doesn’t know what is going on within the heart of each person? Stop worrying so much about others, and work on yourself.