This is not true, Sigalet is not the best but he is not the worst. He has had crap goaltenders to work with.
This is the stats of goalies he worked with.
He was hired in 2014.
2014/15: Hiller 2.36 / .918
Ramo 2.60 / .912
2015/16: Hiller 3.53 / .879
Ramo 2.63 / .909
2016/17: Elliott 2.55 / .910
Johnson 2.59 / 9.10
2017/18: Smith 2.65 / .916
Rittich 2.92 / .904
Hiller’s career averages: 2.55 / .914
Ramo’s career averages: 2.85 / .906
Elliott’s career averages: 2.47 / .912
Johnson’s career averages: 2.66 / .909
Smith’s career averages: 2.71 / .912
Rittich’s career averages: 2.82 / .910
Can they better, yes but they were close to their career numbers.
I don't know much about the Calgary goalie coach at all, but Calgary has had some poor netminders over the last several years, but they were usually around where they were in other places, just like you pointed out.
Hiller had his best season in years the first year in Calgary, before having probably the worst season a goalie has had this decade. Perhaps he wasn't as bad as he played that season, he probably wouldn't have been THAT bad if he played again in the NHL the next year, but it's also possible that his NHL career had just reached its expiration date.
Elliott continues to be what he was in Calgary in Philly, and what he was before he was in St. Louis. The truth is that this is a goaltender that only played well in St. Louis. He never had a good season outside of there and he's been in the league for a decade.
Smith played right around where he was in Arizona, perhaps a bit better last year, and he hasn't even played 10 games this year yet.
Ramo was mediocre, but not nearly as terrible in Calgary as he was before he originally washed out of the NHL when he was in Tampa, before he returned to the NHL for a few years.
Johnson has been a career backup, who has fluctuating numbers from year to year, but he was actually no worse in Calgary when he played a heavier role than he did most seasons. He's certainly had worse seasons on other teams than he did in Calgary.
I do think Calgary needs a more stable goaltender, as Smith is almost to the end of his career and Elliott was a complete bust for them, even though I initially liked the trade at first. I think I liked the trade for them when it happened because I thought he legit improved over the years and I don't really believe there's a such thing as a system goalie, but I think that if there is, Brian Elliott definitely one of them.