I've said what I'm about to say here in many ways over the last week or so. I'll try it one more time because I think that until you answer this question the discussion is meaningless.
In early to mid May 1941, the historic Stalin realizes that the Germans are going to invade sometime in the summer of 1941, no matter what he does, no matter what political maneuverings he performs. That's the POD we're discussing.
Now, here is the crucial question: He reaches that epiphany and does what exactly? What would the historic Stalin do in those circumstances and when precisely would he do it?
Keep in mind that as of early to mid-May he won't have an exact date for the attack. Well, actually he'll have several exact dates from various sources, ranging from May 15 out into late June.
Keep in mind that nothing Stalin does is without its cost.
Want to send factories east en mass starting in mid-May? The sequence is: (a) Shut down production in that factory for an extended period of time while the machinery is packed up. (b) Tie up scarce railroad tonnage to send it east, which disrupts the flow of material to the factories you aren't shipping east. (c) Unpack it and get it set up again. Oh, and add in the cost of building the new factory buildings in the east and setting up housing for the workers you've uprooted. The process takes months. How long did it take uprooted factories to get going again historically? Four months? Six months? While we're at it, add in the cost of building a transportation infrastructure in the east and transporting raw and partially finished materials there. And, add in the wear and tear on a Soviet rail system that was rickety and inadequate to begin with.
Bottom line: Start sending factories east in May and you don't have as much of the crucially needed production in the summer and early fall of 1941. Granted, you potentially have more production late in the year and in early 1942, but you've got to get through the summer first.
Want to mobilize more troops in mid-to-late May 1941? Okay, so the process is: you take the peasant out of his field (in planting season) or the factory worker out of his factory (while you're frantically trying to increase production to supply the armies you already have), you hand him a uniform and maybe a gun if you have any to spare and send him into your already overloaded training system. So, you've reduced food production-not a good idea since the Soviet Union was chronically short of food for the first couple of years of the war, or you've reduced industrial production by whatever the mobilized soldiers would have made.
You've made the Red Army bigger. Have you made it stronger? Not unless you have enough trained officers to tell the guy with the rifle what to do, enough trained logistics people to get food and ammunition to him in a fast-moving, chaotic situation, and enough transportation to keep all of the necessary logistics coming to him. Starving guys with empty rifles aren't going to stop a panzer division.
Stalin's Reluctant Soldiers claims that the Soviets didn't have enough rail or truck capacity to supply the troops they already had at the front on an ongoing basis, which is probably why they stockpiled large amounts of ammo and parts near the front.
Want to put troops on a war footing? When is he going to do that? Mid-May? He doesn't know the exact timing of the attack yet, and as soon as he changes something substantial we no longer know it either. Put the troops on high alert in mid-May and if the attack comes on June 22 the front-line troops have lost a month of much needed training. They've also been in the field for a month or more, anticipating an invasion at any time, which means they're going to lose some of their edge. Having him wait until mid-June to put them on alert is a cheat. The historic Stalin could not know the timing of the attack well enough to get the timing of his response correct. Granted, in this case the lost training time might be worth it, but as we add in a plus for the Soviets for being on the alert we shouldn't ignore the associated minuses.
Again, the crucial question is what would Stalin do and when would he do it?