Those $543 savings on TCO that IBM published in 2016 were not per year, but over a four year lifespan. Also, it was not $543 per Mac, but between $273 and $543 depending on the model.
That is still quite a bit of money on average, but one should also keep in mind that:
a) they were comparing fairly different types of hardware (e.g. the biggest saving was MBP13 vs Lenovo X1 Yoga - the latter being a 2-in-1, not exactly the same use case),
b) they were extrapolating the Macs' maintenance costs based on one year of deployment and comparing this to the known maintenance costs of old Windows machines,
c) the projected savings included the estimated resale value after four years, and that was with 2015-Macs; will the current glued-up and soldered Macs keep a similar resale value, especially once the keyboard replacement program is over?
d) they included various additional software licensing costs that they had to pay for on the Windows machines only because they refused to use the built-in solutions. There may be good reasons for this, for IBM, but it seems a bit dubious to include that in a general Mac savings estimate - few people have the specific corporate software requirements of IBM.
Overall I find these estimates too vague, with too much potential for fudged numbers, to use them as a guidance for my own purchasing decisions.