Route caching gives a boost to speed tests and big file downloads in the same way because of how it works. So yes, big file downloads to one system will also decrease in speed in v7, but you are not doing big file downloads all the time like that. Where route caching starts to really harm the performance of the device is when you have a bunch of users behind it going to a bunch of different websites and other online things. In RouterOS v6 most of this regular browsing traffic will miss the cache, and the cache harms performance more than helping. That is why it was removed from the Linux kernel nearly a decade ago.
Those test results are on RouterOS v6. As MikroTik has been revising test results for RouterOS v7 they are often 20-50% lower than what they were on RouterOS v6 for the same device.
Please see this for more details: CCR2004 High CPU Usage ROS7 - #9 by raimondsp