“This all boils down to something that I call principle-driven design. As stated, some lean UX is better than none, so applying these principles as best you can will get you to customer-validated, early-failure solutions more quickly. Rules are for practitioners who don’t really know the value of this process, while principles demand wisdom and maturity. By allowing principles to drive you, you’ll find that you’re more nimble, reasonable and collaborative. Really, you’ll be overall better at getting to solutions. This will please your stakeholders and team members from other disciplines (development, visual design, business, etc.).”
As there is always UX, there’s always lean or fat UX.