Possibly. Lexapro and Paxil (paroxetine) are both effective for depression and anxiety. Some people do not tolerate side effects of one or another. Others don't respond to adequate trial of maximum doses. Then a switch is indicated. Before switching, your doctor should adjust the dose for a while to check for better effect and diminished side effects.
Possibly. Basic medication 101 says that there is only one way to know for sure how a person will respond to medication - take it. Clinical judgement can be quite good but isn't perfect. Before Lexapro it was true that paxil, (paroxetine) though prone to many side effects, was and still is one of the best meds for social anxiety and depression. Withdrawal has always been a problem with it. None have proven better.