Yeah, it's more or less the unavoidable sin of most "tactical"/"tech" vests out there; they need to be bulky enough to hide the contents, so more padding and a warmer garment. Great for autumn or a well air conditioned office, not so much for summer.
Outdoors/fishing style vests tend to be built lighter and with more ventilation, making them more suitable for the summer, at the cost of looking like you're wearing a fishing vest (a deal breaker for some).