Strictly speaking, of course there is no such thing as objective review, as every personal opinion is defined by one's own tastes. Bias is built-in.
As you said though, every artist has to deal with this with every project they put out. But by far, Zack has been the most used figurehead to be painted as an exception in that he "unfairly" gets the most negativity thrown towards him for "no reason". And that I simply find fascinating. 
Never mind that critics have little time to focus their negative energy on a single person, but Zack isn't the only artist to have consistent divisive or middling reviews over the course of their career. So why does the discussion ultimately always boil down to Zack's films not being judged fairly? Why is there almost never a fanboy consensus that his style is simply not the type to unite audiences, and be done with it? It's not like he's a newcomer. He's been doing this over a decade. At some point I would think people would come to terms with how critics and fans are receptive to his films.
If one were to take a collective opinion of an artist/performer who had consistently been garnering rave reviews over their lifespan, it would be baffling to presume there was an unfair confirmation bias in favor of their work over others. Same should apply for the opposite. After a certain amount of time, I don't try to analyze ulterior motives (consciously or not), but just a present fact of "it is what it is".
		
		
	 
Like Bay, the movies unite audiences just fine. The discussion as far as I'm concerned is that of an extremely finite amount of the audience we like to call critics. An artists makes something for himself and his audience and whether critics accept or understand this is what it is. Jackson Pollock could tell you all about that, seeing as how critics took a while to decide what his audience already knew.
If everyone that loves nolan has been doing so from a place of bias that could easily be questioned too if someone wanted to I suppose. The idea that it doesn't exists is the issue. What arbitrates this is the masses, an entire world of biases from every which way makes it then as fair as one could ask.
My measure of accomplishment in art, is the communication of finding an audiences and speaking to them. The kid that can paint his mother's favorite crayola at will. The techno dj that can captivate an entire generation in ways mozzarts old stuff does absolutely nothing for. Seeking out the bias and catering to those people, the mastery of art is connecting to an your audience in my artistic opinion. Your audience likes to laugh, you make them laugh well vs make a so called 'good movie' by whomever at the time decides what that is. Why we let some tea spoon of the world audience somehow let their personal opinion decide any of these conversations...I'm not really cool with but that's beside the point I suppose.
As for why the discussion has brought this upon Zack and no one else. I have a feeling it might have to do with the fact that this discussion is about this his follow up to his last film. Otherwise people would be bringing this up on some other person. Some people don't like his style and they are bound to not see past that again(admittedly) regardless of if the movie is 'worthy' of praise or not. It happens. That it happens with critics and we can't see past that enough to not let them as in JRob here, inform our discussions in this place..again not a fan. Is what it is as you say. I'm not really one to bring it up.   
	
		
	
	
		
		
			Spider-Man 3 faced Shrek 3 and POTC3 in its second/third weekend. It doesn't get much bigger than that. Yet all 3 performed wonderfully at the box office.
		
		
	 
Memory serves, spm3 didn’t have much competition in it’s second week. That alone is the crux of all of this, for the later you face big competition in your run the better for you. It’s far easier to deal with a mega movie cutting your 5th weekend hundred thousand in half vs a mega film cutting your opening in half and thus on. The more time you have to make your big money in peace the better. Point being, not having your second weekend kamikazeed is worse than having your third.  
Second point, did any of these 2007 films face bigger than 145 million worth of direct and diverse competition in their second weekend? Building off of the first point, when Spiderman 3's third weekend did happen, there wasn't 145million worth of direct competition cutting it’s legs off before it even got started. 
Moreover, the idea that facing off with more than one film with more than one of your demos being far more difficult than a solitary competitor is crucial in any of these comparisons. It's like if you have a film out, and people walk into the theater and see another option, it's probable that they will still choose your film if they don't like that other one. Now if you give them say 5 other big options all different types, the probability goes down: "Oh well I'm not feeling harry potter...but you know that winter soldier is also out so maybe we should watch that instead of Jurassic world, nah I wanna see a big comedy but luckily hang over isn't out so perhaps we can see that other thing from last week fine...." Point here being people that didn't watch shrek that third weekend were more likely to watch spm3 than nothing at all…vs the people that opted out of monsters U, instead watching WWZ over MOS.
Lastly, This idea that mos would have made more if the audience liked it better. Yea no kidding, name a movie where this isn’t applicable. If Avengers had more people enjoying it, it may have made starwars/avatar let alone JW money. The point is how much did it make. Last I checked approaching 300mill isn’t all that likely for many cbms. I feel like if the movie made 350 then people here could still claim that if it wasn’t so divisive then it would have made more like 400mill.. 
At what point does the domestic haul tell us if people liked it, if it’s making this much more than the average non event cbm, than maybe people liked it, more than the last one anyways. If people liked it more is always in the heavy subjective realm, again see Jurassic World, could have made much more if peopled liked it. What isn’t as subjective it the clear indicator of competition for one can imagine a scenario in which no other movies that year let alone that weekend opened and predicted some sort of result. As for if people liked it or not....I can already see the RT argument rolling in peoples minds.. 
One needs to ask themselves not if all those 2007 films made money, clearly they did, but rather how much more any of these films would have made with less competition. All those movies were big closers to mega trilogies so perhaps the numbers they pulled in is technically on the lower end for them vs what they could have made with no competition. We've already seen the difference between MoS' numbers and a superman Reboot with far less comp. All those 2007 examples could have made more, I argue this in light of how much more each of their prior sequels made, films which themselves in fact and truly performed ‘wonderfully’ as you say. About a hundred million more it seems... With that and to answer your proposition in simplest terms, perhaps competition did play a role, I wouldn’t rule it out.