shortof, you are right that unrelated acquissitions can be disastrous BOT ONLY if the buyer attempts to run the company or integrate it into the mother ship. If Warren buys Davita he will leave it alone and let the management run it. Like he said "If the manager calles him for help then both are in trouble"
Did your valuation take into consideration that DVA is buying physician practices doing dialysis & is setting up a specialized pharmacy business serving dialysis patients ( on top of their core dialysis business) ??