> It would be interesting to see what the corresponding figures are like for on-prem […]
You won't find any, not easily anyway. The world of enterprise SaaS follows a different business model that I refer to as «hiding the dead horse in the cloud» and holding the customer to ransom.
The premise: the customer is already locked into the wares the vendor supplies, and the customer can't easily migrate away from the product. Oftentimes, the product is also ridden with the technical debt, but it either has a feature critical to the business or there are multiple business (and technical) processes that have a deeply ingrained reliance on the product. It is either the data or the integration with the product. Regularly both.
The vendor repackages the product («the dead horse») as a SaaS, rolls it out into the cloud (the act of hiding the said dead horse), bumps prices up and slips the bill under the customer's front door (the ransom). Cloud costs are passed onto the customer at a markup. The product (and sometimes the customer) might get minor tangible benefits from the repackaged version, e.g. improved availability and reliability, although even that is not always the case. SaaS products typically do not use native cloud services, they run on EC2 instances (or their equivalent in Azure, less often GCP) and are cobbled together just enough to make them not fall apart.
SaaS, as a business model, is not about the engineering excellence most of the time. It is about squeezing the last drop of blood that there is left in a legacy product, now being offered as a shiny-shiny SaaS version («hey, lookie, we are also int the cloud!»). This is the reality.
The theory is somewhat different. In between 2000s and 2020 (approximately), vendors used to tailor their products to specific needs of each specific customer which increasingly became difficult to maintain, update and upgrade as there would be no single product titled «ABC», there would a «ABC customised/hand-rolled for customer 123», «ABC customised/hand-rolled for customer 456» and so forth. So the original premise of SaaS was to have a single version of the product for ALL customers that exposes simple data centric and whatever other technical interfaces that the customer would hook into. The enterprise world does not work that way, though.
There are positive exceptions in the world of SaaS, and almost all of them are in the startup universe and outside the enterprise.