I have to disagree. Completely.
First: Your theory isn't new. It's been discussed to death here and elsewhere.
Second: There's no evidence that content creators are actually leaving the Mac. It's easy to look at the new machines and Apple's trends and conclude that, but go look on Youtube at any major content creator. FCPX is still popular. If not, Adobe on OSX is still very popular. I'm not suggesting that no one has left, but I don't think it's significant enough to move the dial.
Third: There is little evidence that their dedication to professional machines is wavering on a systemic level. Removing the 17"? Come _on_. That had to have been their worst selling model; anyone who needs a screen that large would just plug into an external monitor. Discontinuing the Mac Pro? It isn't discontinued; they've actually promised updates to desktops soon. Yes, they let it get old in the tooth for a while. But I will be willing to accept this argument only if 2017 passes us with no upgrades.
The MacBook Pro has its issues. It is, absolutely, ahead of its time with its port selection. The only port it is truly lacking that professionals should miss is the SD card slot, and I will grant you that is unfortunate and unlikely to be fixed. Weak processors? Go look at the Intel ARK and tell me what mobile processors Apple could have put in this machine but didn't. This is Intel's fault, not Apple's. Weak graphics card? Yup, I'll give it to you, a GTX 1050/1060 would have been incredible. No 32GB ram option? Unfortunate.
But the issues I am describing are not systemic. They are going to be fixed in the next gen model. The pains you're seeing today are just the "early adopter pains" we get with every brand new Apple product.
Fourth: I can literally tell you why their sales dropped 10%, right here. Ready? No MacBook Air refresh. No iMac refresh. No Mac Mini refresh. That's it.
Apple's Mac sales are not, in _any_ way, propped up by professionals. Don't flatter yourself and this industry with moving the needle at all on Apple's bottom line. They are propped up by average joe consumers, and this market segment was hurt very badly in 2016 through Apple's unwillingness to cater to them.
Apple's lack of updates to the Mac Pro has been unfortunate, but hasn't hurt their bottom line. Apple's lack of updates to the MBA (last update: March 2015), Mac Mini (last update: October 2014) and iMac (last update: October 2015) are literally what is causing this 10% drop. The machines are stale, and people know it.
Apple fixes this by refreshing their desktop lineup (which they have literally said they are going to do, and Apple _never_ tells us anything) and dropping the price of the MB/MBP (also seems likely).
Finally: I would remind you to not confuse "Apple is giving up on creatives" and "everyone else is getting better at servicing them." Microsoft has been doing a stellar job lately, and Windows and its accompanying hardware is better than it has ever been.