I have made beers with 20% crystal malts. That does definitely create a sweetness in the beer. My understanding from Denny Conn is that Rogue Brewing uses up to 30% crystal in some of their brews. So it can be done successfully. I can't say that I prefer beers with that crystal content, but they are palatable.
The high calcium content is a result of the high sulfate that the brewer wanted in the water. Calcium has little flavor effect. But the sulfate will definitely have a drying effect on the beer. Maybe that is used to counter the sweetness from the high crystal content. I have not tried a sulfate content over 300 ppm, but Colin Kaminski says he prefers the level at over 600 ppm. He said his customers generally don't like that much sulfate though. I can't recommend it, but I won't dismiss it as folly. If you are adventurous, try it yourself.
The big problem with this recipe is that there is no alkalinity in the water to counter the huge amount of very acidic crystal malt and the very high hardness. This mash will DEFINITELY have a mash pH that is less than 5. The beer will be noticeably tart and thin, but that might mesh with the high amount of crystal malts. If the sparging water has high alkalinity, it might help increase the pH of the wort in the kettle to a more normal value. But this pH thing is a big red flag.
Danger, Will Robinson, Danger!