The boutique idea is about control. Lange is going to shift to a mostly all boutique sales model. There will be very few ADs left if any. The boutiques are a VERY HIGH COST and FINANCIALLY RISKY endeavor. Obviously a multi-brand jewelry store is more efficient. Imaging three separate stores for burgers, soda, and French fries. Obviously combining them into one is more efficient for everyone - but the expert making French fries will say that his French Fries don't take center stage anymore...
Lange is going to a boutique business model. Some boutiques will be 100% corporate operated. Some boutiques will have a partner operator (normally another jewelry or watch store). All staff will be rigorously trained about Lange watches and what make them special and how Lange even differentiates from the other "top level brands" like Vacheron Constantin, Patek Philippe, and Breguet. Lange's Management Team noticed that at multi brand stores, the salesperson was happy to sell any brand - as the salesperson got a commission from any brand as long as the client bought something. Most people have heard of Vacheron Constantin, Breguet, and Patek Philippe and have not heard of Lange and thus probably bought one of those three Swiss brands. Thus, the salesperson didn't present Lange in a special light nor tout what made Lange special. The salesperson at a multi-brand store also wants to present all brands as excellent brands and to be politically correct. For the salesperson to say Lange does things this special way implies that the other brands are less special and inferior which is not something the salesperson wants to convey. Thus, a mono-brand boutique can tout its brands' speciality to a higher degree without political pressure.