FR was problematic because the FR networks were oversubscribed, which was actually one of the benefits of the technology. The tech support for FR was also lackluster at best. The nice thing about FR was that you could aggregate multiple connections on one piece of equipment and pay based on usage rather than committed bandwidth.
The over-subscription was definitely a problem. The ISP I worked for had a fractional T1 in their main POP for frame relay (512K or something?) There was about 4 to 5x in bandwidth needed for customer connections, assuming 100% utilization. During peak times in the evening, the FR was massively overloaded and ping times would get into the 100's of milliseconds (normally it was 10 to 15ms IIRC.) The connection never went down though, even when they were slow.
