> By removing something from the seq it needs to be reordered. ( shift elements > )
If you don't need the ordering, use [del](https://nim-lang.org/docs/system.html#del%2Cseq%5BT%5D%5BT%5D%2CNatural) Try the testing by choosing the span element randomly instead of pre-determined value. It will ensure compiler couldn't optimize the entire loop-deleting. Or from value from program arguments. Also object (pretty much) possibly allocated on stack while ref allocated in heap. Stack allocation is always faster.
