The All Stars are on Disney Property. You use the very reliable Disney transportation system and once on your way, only take 10-15 minutes to get to the parks. The roads on Disney property dont' seem to suffer the same traffic congestion the other surrounding roads do, and it's a fairly painless, albeit often crowded, trip.
It's a great resort to stay at.
As far as staying in Kissimee, you would have to get through traffic to get to Disney roads, then head to the resort, park in the huge lot, then tram up to the front gate of the park. The Disney bus system pulls up near the front gates. Sorry, but I'm a little biased towards the simplicity of staying on site. What the
Travel Agent is telling you isn't quite right.
Also, beware the off-site hotels who have 'free' transportation to the parks. Quite often, they are not even close to running as many busses to and from as Disney does, and at the end of the long day, you really don't want to be waiting an hour or so for a bus to pick you up for the commute home.