runs like a vac leak

Thats right. And if the cylinders have been washed clean by a poor tune, it will be worse.
The compression test tells one PART of the story.
The cylinder leakage tells another PART.
Together, a pretty good picture emerges as to the entire state of the swept volume and chamber.
Consider this;
a leakage test will not see anything below the ringpack at TDC, but a compression test will find a wrist pin groove real quick.Or a compression test at 155psi might be fine, unless a Leakdown test shows every valve is leaking or every ring is worn out to the same degree.
I dont tune engines anymore for guys that refuse these tests as part of my tuning regimen.I have chased my tail too often in years gone by. This is particularly critical on small, highly stressed powerplants; like snowmobile engines.