If you are ruthless in cutting unnecessary spending, you're probably going to end up cutting salaries, firing people, or going cheap on other things that actually affect staff, which is likely to be your largest expense.
The quote was either phrased worded or the author doesn't understand the word. Ruthless people are not nice.
Like you said it's unnecessary spending. Firing a slacker can be both ruthless and nice (towards employees that put in real work). There is no obligation to pay people and no right to be paid. Cutting wages is not some horrible or cruel act if it's done for good reasons.
but the point is that "ruthless" doesn't mean "great at seeking out waste" but specifically "having no compassion". it applies only where compassion would reasonably be applied by others.
The quote was either phrased worded or the author doesn't understand the word. Ruthless people are not nice.