Panama City is about 50/50 English/Spanish but that ratio gets much worse once you leave the city. My Spanish borders on basic to average. I would probably become fluent within a year of living in a Spanish community. I did find it odd that one of my uber drivers, after I said hello in English. He said in Spanish. I speak English but I'm not going to speak it. lol ok.
Panama City is hot. The weather in Boquete is wonderful but man if you are retired and in your 70s etc and you need any kind of major medical it seems like it would take hours to get back to Panama City. I have no idea what medical is like in David or Boquete. Now they are expanding the airport in David to handle bigger planes. They can already land 73's but my guess is that want to get into the 78s so they can get direct traffic from all over. That might change the medical issue but that's going to take a while.
The biggest benefit to lving in the city is not only access to the US but PTY is such an international city that you can probably fly almost anywhere in the world direct.