What you say is very true. And LVMH also owns Moynat, Tiffany, Fenty Cosmetics, Guerlain and even newer ventures like La Bouche Rouge too. Kering also owns Brioni, Boucheron, Pomellato, Dodo, Qeelin, Ulysse Nardin, Girard-Perregaux and linked to Christies auction house too and set pre-loved prices via estimates. The expansion isn't over yet either, I'm sure they are looking for replacements for Stella McCartney and Sergio Rossi too because they see LVMH as the competition and LVMH has expanded hugely recently, 'betting' on jewellery and cosmetics (top and tali of the luxury chain).
Great to see a new member ask such an interesting question.
I'm not 100% sure what is meant by cheapening, but I think I know what you mean. Prices certainly seem to rise with increasing frequency and in unison, I doubt very much whether the increases are going towards labour or materials, just expansion plans and more and more company acquisitions.
However, I don't see a homogenised design aesthetic over all LVMH businesses or Kering, although I notice that I choose jewellery from other companies besides Richemont owned which tend to be smaller (apart from Hermes). I need to think about it more.
There are some benefits of being in a group. It can increase accountability of supply chains and manufacturing standards which can benefit those companies and their customers in terms of sustainability and consistency. These parent companies have so much power in the industry it would sheer folly to risk their reputations. Also it can help start ups and new businesses. Fenty was able to grow huge very fast because of LVMH money and muscle, and La Bouche Rouge has very few of the start-up problems that most niche companies experience. The wave of publicity that accompany acquisitions can also boost those companies, Pomellato seems so much better known under Kering even though their aesthetic hadn't really changed (fans please correct me if I'm wrong) and I doubt Alexander McQueen would have become the global brand (from 2002) and weathered the storm of the designer's sad death in 2010 without the clout of Kering (Gucci Group as it was) behind them.
Most of these brands are like department stores in themselves. A McQ, YSL and Bal are primarily fashion houses, so of course it's handy to have factories that can tan leather and make bags and accessories (Gucci owned) and have Kering eyewear across all brands. This always happened in smaller ways (Gucci always outsourced material bags and worked with other specialists) but the vertical and horizontal integration is much closer within many of the brands of the same parent company.
There are plenty of other amazing luxury houses for bags, jewellery etc that are not owned by the big 3 (and are not H). Def some you should check out, which one(s) obviously depends on your own aesthetic sensibility and where you live. I think it's great to support independent businesses.
Since I wrote this LVMH pulled out of buying Tiffany