asp.net caused mysql 99% usage
There may be various causes for this difference, but the first thing that comes to mind is that the second configuration is tuned to use less memory (e.g. innodb_buffer_pool_size, tmp_table_size). Therefore, it may need to use more disk IO to process the same amount of data. CPU has to wait for disk operations to complete before it may proceed to the next chunk of data and hence it becomes underutilized if there are lots of them.

You may try to confirm this conjecture by establishing disk performance monitoring approximately like described in https://blogs.technet.microsoft.com/askcore/2012/03/16/windows-performance-monitor-disk-counters-explained/ .

And I would say 100% utilization of one CPU core is a normal thing with bulk operations in MySQL. The engine doesn’t have much parallelization so it generally can’t use more than one core per session. Lower utilization during bulk operations (e.g. mass insert) means there’s non-CPU bottleneck that needs addressing (because it makes the same operation take longer). You may try to figure out if that’s the case by comparing the time it takes the test script to complete in the two environments.