OoO came about after multi-issue architectures were starved for instructions to execute due to on-chip blockers like execution unit availability, data hazards, pipeline bubbles, register availability, branching, cache ports. You can call those input data availability problems but it's not availability from offchip memory. So in actual history, yes it was for parallelism (keeping multiple execution units busy).
OoO did have the side benefit from possibly executing past a few memory stalls but those were secondary. OoO reodering resources were sized for addressing the stalls from on-chip timescale things. Today the resources are bigger, but even bigger is the relative memory latency (how many insns you could execute in the time it takes to service a main memory fetch that your pipeline depends on).
OoO did have the side benefit from possibly executing past a few memory stalls but those were secondary. OoO reodering resources were sized for addressing the stalls from on-chip timescale things. Today the resources are bigger, but even bigger is the relative memory latency (how many insns you could execute in the time it takes to service a main memory fetch that your pipeline depends on).