They're off to the side due to insufficient space to put them on top of the CPU/GPU/SoC. So all laptops place the fan off to the side connected to a heat-pipe which is used to draw the heat away from the CPU/GPU/SoC to the fan where it can be exhausted.
Yes, because it has a systemboard to support the A13 SoC and it's associated RAM and other required chips. I mean the thing technically would be a computer if you could jailbreak the SoC and run something like Ubuntu 20 like some kid did with their iPhone 7.
Apple does not "over engineer". Over-engineering just wastes money making it more expensive to manufacture.
They engineer exactly to what is needed to support the functionality the product offers.
Apple has not run external power supplies to their standalone displays since the Cinema (HD) displays of the early 2000s which used ADC.
Once Apple launched the 24" LED Cinema Display in 2008, the displays had an internal power supply and the ability to power a Mac laptop (up to a certain wattage) via either MagSafe (LED Cinema Display and Apple Thunderbolt Display) or via ThunderBolt over USB-C (Pro Display XDR and Apple Studio Display).
Well there were rumors of a "taller Mac mini", but that was what everyone assumed it would be - a Mac mini with more ports and an M1 Pro/M1 Max.
So the Mac Studio was rumored and leaked before it launched - we just did not know it would be called Mac Studio.
Ross Young's sources are in the display channel so all he sees is LCD panels. So he was seeing new 27" 5K panels being developed by LG Display and naturally assumed they would be for a 27" iMac. Let us not forget that back in 2020 Ming Chi Kuo first leaked that LG Display was working on a 27" MiniLED panel and he assumed it would be for a refresh to the 2017 Intel iMac Pro (since Apple had not yet announced Apple Silicon for Mac).
It was only as the Apple Studio Display went into production did his sources say "yeah, this is a monitor, not a PC" which is why he updated his tweet to say this new panel was going into a monitor and not an iMac.
He is still evidently still getting leaks about the 27" 5K MiniLED with ProMotion panel, but now he is hedging his bets and saying it will be either in a new iMac or it will be in a new standalone display.
Despite their money, Apple does not have infinite engineering talent and they especially do not have infinite management oversight due to their management structure which favors the most senior managers overseeing
all hardware and not specific hardware silos (Mac, iPhone, iPad, Watch, etc.).
So when one Mac product hits a snag, they have to pull resources from other projects. Laptops are the most important, so they get all the engineers they need. When the laptops are sorted, then they go with iMac since it is the second-most important. So the 24" iMac suffered from a lack of engineering talent because those assets were working on the MacBook Pro 14"/16" and M2 MacBook Air (as all three were designed in parallel per interviews with Apple executives). And once the 24" iMac and the MacBook Pro 14/16 were done, engineers were freed up to work on Mac Studio and get it out the door.
By your own argument (and historical precedent) that Apple designs all sizes of the iMac together, there is no sense to Apple pulling engineers from a 27" iMac to get Mac Studio out the door. They would have worked to complete the 27" iMac to complement the 24" iMac and
then returned to work on Mac Studio.
The leakers who have consistently claimed a larger 27" iMac is coming only to see it not are, IMO, just trying to save face by claiming "Apple doesn't want to cannibalize iMac 24 / Mac Studio / Studio Display sales" or "this new iMac is being delayed so it can use M2 Pro / M2 Max" so they can kick the can down the road another year and hope that, like the square-sided Apple Watch, it actually happens so people continue to pay attention to their sites.