Based on my freewheel surgical experience, there's really no internal difference (mechanically speaking) between Suntour and Shimano freewheels. Even across different models. The Winner line bodies are designed to handle more cogs and a 13 tooth high gear, but the internals are the same, just a different size.

My guess is more than anything else, is a Perfect and Pro Comp FW were used on less expensive bikes, and generally speaking, did not receive the same care and attention. Therefore, they sat out in the weather, were rarely cleaned, ran the same dirty chain for decades, and thus are more prone to failure.

Here's a picture of three different FW bodies ready for reassembly, can you tell which is which?



Two Shimanos and a Suntour Alpha.