The impact has been negative for the following reasons.

First, the groups made whisky into a luxury good, expanding the customer base away from the amateur who bought the bottle for its contents. In certain industries, a bubble is a good thing as it draws a lot of talent into the industry. However, whisky is supply constrained - the older stuff is limited in quantity by the smaller market when they were bottled. The result has been a global rise in prices and cut in quality. See the NAS on all Japanese entry and many mid-level bottles, and Japanese houses importing after exhausting their own reserves; or the newly purchased and restructured Mortlach, which is also NAS despite its premium price tag. There is also a shortage of actual casks, particularly sherry, in this case limited by the Spanish wine market, leading to "creative" finishes or sub-par casks being systematically used to meet demand.

Second, from the POV of the house doing the acquisition, a brand has to fit in a portfolio of brands, and this can lead to intentional downgrading. For a well-known, non-whisky example, Longines has suffered post-acquisition, because the Swatch Group has decided that Omega should be their flagship mass market premium brand. You do not retain strategic independence or the ability to just "produce good stuff" after acquisition - the so called synergies can be negative for you.

Third, the massive influx of money into the industry has all but killed the apprenticeship model which is still alive and well in the wine world. If a distiller should show even a hint of skill, they will be rapidly discovered and acquired before they can grow. There is a parallel today in the startup world where everyone seems to be gunning for acqui-hires rather than building a company the scale of PayPal or Amazon (and WhatsApp showed that everyone has a price, and the industry will pay it); and Google etc.'s talent safari leads to a corresponding drop in great people contributing to open source research, which harms the commons (the advancement of collective human knowledge is slowed). There are hints of what could be; for some reason Australia has somewhat escaped the sights of M&A divisions, and Tasmanian whisky, not exactly the most well known thing to put in your shelf, is bid up to over $500/bottle (in Heartwood's case, for example) by amateurs with means. I wonder what a whisky market closer to France's wine industry would look like...

Fourth, the Veblen good buyer may actually have so much impact on the industry as to change the product itself. The explosion in popularity of Bordeaux premier cru wines in the new world as part of a well balanced portfolio has led to a move towards massively tannic wines that lack the balance and elegance that used to be prized amongst the French experts (who by and large are priced out anyway). We have witnessed a similar drive in whisky towards peat, not just in the Scottish islands but globally. Peat can be measured, and bigger is better, after all: just ask Ardbeg (owned by LVMH).

Fifth, the marketing money screws with information discovery. The big brands can completely cover any buzz about independents with noise by paying for thousands of journalists (whether experts or not) to write reviews on their products, by sending free samples to anything that looks like it talks about whisky, by organising frequent events, through the usual SEO Google-undermining process, and so on. Censorship through abundance. Until one finds a good gatekeeper, it can be difficult to find good value, and most gatekeepers are co-opted.