it sounds like you're comparing apples and oranges to me. they're both fruit, but that's about as far as it goes.
and your real beef seems to be that you cannot adapt your environment: that just sounds like you have an immature host.
but neither with jpgraph nor with flash charts do you need to 'download' anything, in the sense of installing. these packages are simply script libraries that you copy and paste into your webspace and then use like any other php script.
As for any web application, the complexity of the application mirrors the complexity of the API. JPGraph's API can get quite complex if you want to create complex graphs. but for simple graphs, i wouldn't have thought you could get something much cleaner. It only needs to be told the y values, x values and the type of graph you want to output. pretty straightforward, no?