He is representative of the Pharisees (among others), but not as an “evil hypocrit.” He is the representative of every hard-working, right-living, faithful person who has ever found himself resenting the salvation God offers to the wanton, lazy, or otherwise “unworthy.” There are plenty of Christians who have fallen into this trap at one time or another. In fact, you can make the case that each of us has, at one time, played the role of the younger brother, and at others, the older.
It’s worth noting, in addition, that the older son does not lose his inheritance because of his resentment - the father says “everything I have is yours” (Side note - sin still has temporal costs - the younger son has in fact squandered his inheritance and the father does not appear to be about to redivide what’s left.) But the older brother is cutting himself off from the joy by his resentment and anger. He could go in and join the party - but he won’t, because he’s too angry.
God wanted to invite all the prodigals into the kingdom. He didn’t want the faithful to exclude themselves.