Only track/treadmill

Hi, Last 3 months I have been doing all trainings on track and treadmill. My paces have increased really good. Did a street HM race recently but didn't perform according to my expectations. I was wondering if the lack of street runs/varying surfaces with some uphill/downhill have made me "weak" muscle wise? Did some easy 10ks <70% max HR in a slight hilly course and it feels harder than same easy 10k on track even with same HR.