I haven't make any claim about 100% effective software. However, one software can be less effective than another. Saying that one is 90% as effective than the other is just to help visualise things.
> what sells in enterprise is marketing and a good sales team, not "effectiveness"
I work for a SaaS company. Our marketing and product teams work hard to convince potential customers that our software fulfills their needs at a reasonable cost.
When we buy services and software we don't look at any of the marketing materials, there are very trough analysis of costs/benefits being made, dollars and even cents are counted. Every cost that can be cut while we can still deliver something to our customers will be cut.