You are right there are also other factors affecting the hashrate like the introduction of more efficient hardware, manufacturing and more importantly delivering these hardware to miners who filled an order a while ago (this could take months).
Correct, and there's absolutely the price as a parameter, but I doubt it's number #1 priority for large farms, which are what consist the hash rate. I'm wondering, do we have a list of hardware efficiency overtime? We can verify that it's the more efficient hardware that drove the difficulty up. I haven't seen miners talking frequently about that.