Not true.
N54/55 are not modular engines. Cooperation with Peugeot was on 1.6ltr 4cyl engines which also proved very durable. On that note, 1.5dci engine by Renault is one of the most durable diesel engines ever built. Just to clarify your assumption that somehow those are "lesser" products.
N54/55 engines have oil starvation issues bcs. inline 6. There is too much of an engine and one oil pickup line. That problem is not present on S55 or N55 in M2, as they have two pickup lines. Starvation issues usually happen with highly modified vehicles that are capable of much more G than designed and only in a left turn. xDrive models are not susceptible since the axle goes through oil pan and basically serves as a baffle.