Out of order execution makes your code run faster like 20x-50x. You can’t produce a CPU without it and compete in the market. There are many variations of spectre and meltdown bugs, some of them might be fixed in the CPU and some in the OS. So, there is no simple answer to your question I believe.
Afaik all spectre/meltdown family attacks are possible even with a single OoO execution. But increasing the quantity(adding more complexity) might cause new batch of security issues ofcourse.
