Comment by eigenspace

Not really a meaningful comparison because you haven't defined how much of a temperature difference versus how much of a water flow difference we're talking about here. But for most people, at least if they take the most basic level of care to not use water at like 85 degrees or 110 degrees, then no, that's just not really true.

There's a lot of folklore out there that's lingered from the early 2000s espresso community where it was widely believed that temperature was the holy grail control parameter, but now with modern instrumentation and temperature probes, it's been pretty much debunked. Temperature stability throughout a shot makes almost zero perceivable difference in taste.

It takes brew temperature differences swings of around 5 degrees Celsius before people can start to notice any difference better than random chance, and almost a 10 degree brew temperature difference before it gets to the territory of 'ruining a shot'.

Meanwhile, very small differences in puck preparation, including micron-differences in grind size, or sub-gram-level differences in coffee quantity have profound differences in flow rate, which has a very strong affect on coffee extraction levels, which has immediately recognizable differences in the produced flavours that a trained palette can reliably detect. This is before we even start talking about channeling which has an enormous affect on the coffee.

Manual control of the applied pressure can and does allow skilled people to compensate for those differences in flow rate, and combined with very basic attention to brew temperature, does help shot consistency.