As an owner I'm somehow biased about my car but putting me aside, I never had a passenger who wouldn't praise the interior's styling and material quality. Even by fanatic Audi fanboys. Also during night driving the interior illumination found approval by most passengers. No one claimed it is outdated or ghastly.
When it comes to the media system which he also blames, yes, it hasn't/hadn't Android 4.4 UI design (4.4 was released on smartphones around 2013/14) but it still is easy to operate and looks more than OK to me. Voice recognition works just great at any speed. And we know the R tends to be loudish at high speeds. Still, it works and entering a destination while keeping both hands at the wheel is easily accomplished.
Flimsy build quality? I dunno. Depends on how you perceive quality. When it is only about some squeaky door handles and a bit cheap-looking plastics in the lower bottom of the interior then most Audi are not better than the R. I challenge anyone to go to the next Audi dealer and check out the newest A6 interior (the newest one, because with the new gen their quality requirements on interior parts deteriorated). It also is equipped with mediocre looking plastics.
The R isn't a Rolls Royce, but it isn't a Dacia either.
But when quality means keeping up a high level of quality of fitment and material surface for a longer period than the first shiny months of ownership, then I salute to the Peugeot RCZ R. I also own a Lexus, so I allow myself some comparisons and references. The pug isn't on Lexus level, but the level it maintains easily outguns its competitors in this price range. My R with almost 200.000 km on the ODO and always rushed with high pace still maintains a flawless interior. I have literally no wear off at any button/surface/whatsoever. Still looking like new. Only on the steering wheel some of the leather shows a bit of wear off. Something like you would see on other cars with only 40.000 on the ODO.
And not a single rattle, clonking or shaking of parts while driving. Nothing.
Only down side is the driver's seat which is a bit thru. But only a bit. Nothing which takes some of the comfort or support of those seats away.
I'm really blown away by the high long-term quality of the interior. And in my opinion that counts more than some shiny plastics for the first months and then the misery of having to deal with worn interior parts.