Firstly, thermogenesis is only about 10% of our total energy expenditure (and it's not like organisms floating around in a tank don't need to regulate their temperature either!).

Secondly, even with the tank model we're talking 3 or 4 calories in/calories out vs. 10/1 (for chicken; you may of course choose some other animal as your baseline if you want to make things look better for lab meat). It's an improvement, but not as significant one as you might think.

Thirdly, there's lots of evidence that the processes I mentioned (oxygen pumping and blood circulation, filtering out toxins from incoming nutrients, filtering out waste, and the active immune system) are a huge percentage of animal energy expenditure. The Wikipedia breakdown of our BMR shows that the liver (responsible for flushing out toxins from incoming nutrients) represents about 27% of the BMR, the kidneys (responsible for filtering out waste) another 10%, and the heart (responsible for pumping blood and oxygen) another 7%. Even if you assume "other organs" (taking up another 19% or so) represent inefficiency here, and the brain (another 19%) isn't needed, that still means that in humans, about 45% of our BMR are devoted to these three functions (18% is used directly by skeletal muscle and is presumably also required in a lab setting). Additionally, from what I read elsewhere, the active immune system represents a remarkably large proportion of animal energy (some 25-30% of our basal metabolic rate!); there may be some overlap with these other organs, but I suspect this reflects a substantial portion of the remaining energy use.

So now we're at somewhere between 50 and 70% of the energy use in comatose animals being taken up by exactly the processes outlined in the article as being challenging for lab meat, not far off from the 50% - 75% reduction we are supposed to get from growing meat in a lab. I somewhat doubt this is a coincidence! It's true that there's extra unnecessary stuff animals do (such as growing bone, physical activity, and thinking), but there's a reason the BMR is such a high percentage of our overall metabolism--this stuff is all really important, and trying to do without it leads to the kinds of issues discussed in the article.

Moreover, even if you disregard the energy expenditure requirements, I think oxygen transport not scaling well with increased container volume (given the physiology of animal cells) is pretty fundamental. AFAIK it is one of the things that historically has made it difficult for animals to get too large. Yeast or plant cultures can get around this because they don't all need oxygen to metabolize in the first place, and have cell walls that can filter out byproducts more much effectively than animal cells can. Animal cells do not, and as noted in the article the lack of cell walls also makes aggressive mixing a no-go. That to me is a big reason for pessimism that I don't think is easily resolvable without significant changes to their cellular anatomy.

All that being said, I'm not saying to give up--I think everyone would love for lab grown meat to work and be at least competitive (on both a cost and energy basis) with "regular" meat. And of course it's possible that we can find more energy efficient solutions to all of the problems I outlined than animals do. But I do think that we should be realistic about the fact that we have no good reasons to think current approaches are going to work, and lots to think they won't, and therefore treat claims of near-term improvements in this field with appropriate skepticism.