You are forgetting about the stative verbs (or whatever they are called) in Hebrew, which don't take the waw between the first and second radical in the present tense (their pattern is xAxEx instead of xOxEx) - ישן, גדל, חסר, ירא but also many more which are used as adjectives, but are technically verbs, which also follow the pattern - שמח, יפה, רעב, מלא, יבש, צמא and many more. So, רזה and שמן also fall into this category and they can indeed be both verbs and adjectives.
Oh yes, you are correct, I forgot about them. It is הוּא רָזָה וַאֲנִי שָׁמַ֫נְתִּי he was getting thinner and I was getting fatter in the past, הוּא יּרְזֶה וַאֲנִי אֶשְׁמַן he will be getting thinner and I will be getting thinner, but in the present הוּא רָזֶה וַאֲנִי שָׁמֵן he is getting thinner and I am getting fatter. Thank you for the reminder!