Unfortunately you have swallowed the leftist propaganda hook line and sinker. Cops are not dealing with ARs and such on any statistically significant level. In fact the percentage of crimes committed with ARs and MAC-10s is so low its difficult to measure accurately. Most cops will spend there entire career and never see any rifle used in a crime much less an AR-15. What you stated simply isnt true.
Maybe I watch too many episodes of Chicago PD, then. They seem to face criminals with military grade weapons every other episode!