Actually B6 is a top level US based carrier despite the fact that they have no BC/FC and that their FF program is limited. They have satisfied customers, great staff when you have to call in (think the horrors of the UA's automated system which dumps you off to an untrained contract worker), an excellent website, etc. Terminal 6 at JFK even has takeaway vegan meals now. Mention legacy carriers to a great many people and a complaint is surely right at the tip of their tongues. Look at all of the US legacy carrier's boards on flyertalk. Even hard core UA fans seem to delight is getting compensation for the many things that are wrong. Get on a jetBlue plane and people are generally happy to be there. This is why I switched from being a UA fan to a B6/VS flyer. I can take higher quality international airlines when I fly out of the country and within the US, unless there is no other choice, I will take B6/VX.

LH wants to partner with an airline that will treat its passengers well and provide connections out of BOS/JFK to where they want to go. Maybe B6 will evolve to offer BC/FC in the future. More international partnerships are already a given meaning that their FF program will offer significantly more benefits in the future.

A UA investment in B6 would be a big mistake. UA reached its apex in the mid-90s and has steadily fallen since. Why try to combine a company with demoralized employees and a management team that is looking to sell off the company with one that is actually trying to be innovative and focused on its customers? LH saw that it needed a quality partner in BOS/JFK and B6 fits the bill.