a few years ago i did manage to get a pm/ba type role at a small-medium size agency. giant mess of a place (norm for that industry i guess) but it was a meat grinder - all about billable hours (which were hard to come by since every project was undersold and over budget), which meant I worked 50+ hours every week with no salary increase or bonus. burnt out and left when it was obvious there was no opportunity there. although to your point the place was a revolving door and SO many hires were gone after 3-6 months, so perhaps ill look for places like that.
No two web agencies are alike. I've known the kind you describe and I hated them but I've known—and currently work at—much more comfortable places. Apply and see how it goes.
