This is a phrase I came across while watching Pokemon in Japanese. The fan subtitles have it translated as "How are you doing now?". However, from looking at a Japanese dictionary, that does not seem to be what it means. I have attempted to interpret the phrase but I could never land on a concrete meaning.
For context, Satoshi tells his opponent (悪いけど派手に倒させてもらうぜ). When he starts losing the upper hand, his opponent says (まあこんなもんよ). I am uncertain if this was exactly a response to Satoshi, but he was the last person to speak to his opponent in this scenario.
The word that confuses me the most is もん. I've seen it defined as stock or goods which doesn't seem appropriate in this context. I've also heard it is used to express dissatisfaction, but considering that こんな must be used before a noun, that does not seem to fit either. Is the phrase slang for something else and if so, why is that?
I'm not concerned with an exact Japanese-to-English translation. I want to understand what is being expressed.