I understand where you're coming from but ...
> There's virtually no competitive advantage to having unique business processes.
I'm not intending to take this sentence out of the context of the rest of your post (on its own, I don't think you agree with that[0]), but I think even in context of "specific to resource planning" there are many competitive advantages that companies pursue.
Take "Time Accounting" for example. I'm not referring to tracking hourly employee hours for payroll, I'm referring to tracking salary employee "project time." Every past salaried position I've had at a company with more than 90 employees had its own custom time tracking software[1]. The first company to do this was a multi-national telecom that I worked for. It was done so that each project could be broken out into its stages and the portion of the employees' salary could be itemized among "Capital Expenses" and "Operational Expenses". This was so important to the company that it warranted a massive development effort along with a corporate initiative to get 100% of time reporting in "on time." They did this as you'd expect a huge company would -- fail to hand in a time sheet on time a few weeks in a row and you'd get dinged more for that mistake than anything else.
The second and third companies ended up "accidentally developing time tracking software" specifically because there was competitive advantages to improving "Resource Planning". It was most helpful to my last employer. Their businesses was creating new products (often hardware/software combinations) for companies. This involved hiring a large number of people specialized in things that had limited cross-over. Resource Planning was predicting when what skills at what level would be available. This, necessarily, involved tracking what time was spent on projects in the past to improve those predictions and ultimately ballooned into a full time management and accounting application for the business (they sold "our time" to customers at the end of the day so it helped them to plan what to charge).
I'm curious -- from your perspective, is it that the competitive advantage is lost "because the tools that everyone is stuck with won't work" if you stray too far from "standardized" or is there another advantage to this standardization?
[0] Unique business processes and marketing are frequently the difference between the #1 and #2 company in a given space.
[1] In one case (about 250 employee global company), the company wrote it as a concept for a future product but once it was available, the existing solution was tossed primarily because the business side really liked the flexibility. In another it grew out of a pet project and became entrenched. At the remaining two, a decision was made to develop something from the ground up.