Concentrate exists to solve a shelf-life and shipping-cost problem, not a flavor problem. It is a compromise, and cocktails made with it taste like one.
What gets lost in concentrate
Juicing, then reducing to concentrate, then reconstituting later strips out the volatile aromatic compounds that give citrus and other juices their brightness. What comes back after reconstitution is sweeter and flatter than what went in, which is why concentrate-based drinks often taste like they need more acid, even when the recipe says they shouldn't.
The tradeoff
Fresh-pressed juice does not keep. That is the entire reason concentrate exists in commercial beverage production. A cocktail base built with fresh juice has a shelf life measured in days, not months, and needs refrigeration the whole time.
Why it's worth the shorter shelf life
For a batch cocktail meant to be consumed within a few days of an event anyway, the shelf-life tradeoff costs nothing. You get the flavor benefit of fresh juice without ever needing the months-long shelf stability that concentrate exists to provide.