In terms of people questioning Sennheiser's expertise at making headphone amps, even ignoring the HEV90, it's an odd sentiment.
Sennheiser is a major corporation who have been making headphones and microphones for professional and consumer markets for a long time. Any expertise they don't already have in house they have the resources to hire. Some of the companies people have glowingly quoted as being the true experts at headphone amp design are very small companies with self taught DIYer at the helm.
Some of those companies make great amps, some make questionable products that have gained favour in a small online community through customer reviews and group think. Not going to say which I think are which, as I'm not even trying to denigrate anyone, but lets just be realistic here.
If Sennheiser want to make a headphone amp, they are going to use credentialed electrical engineers with experience of working for other renowned corporations on similar products. They are going to have all the tools to test and measure and perfect the product they are making. Sennheiser is not a guy sketching out a DIY amp idea in his garage, working by trial and error and judging success by ear.
"Odd sentiment" = different opinion than yours?
It is reasonable to arrive at differing conclusions based on our alternate knowledge or professional experience. Your sentiment is no more "odd" than mine. It is just different.
I have been involved in engineering and product development for large companies for close to 30 years now. Rightly or wrongly, it tends to color my perspectives. I still await the simplicity and success of the staffing a team, integration of new development, resulting in a smooth initial launch of a generation 1 product that you outlined in your post. These tend to happen in the pages of a McKinnsey or BCG PowerPoint strategy decks more often than the reality of R&D and Engineering in corporations.
I also would not confuse a companies size with expertise, experience or design quality. Size can attract talent, but more often provides capital which enables manufacturing approaches and economies of scale. A product developed for Sennheiser will have many commercial requirements that those made by smaller independent companies will not have (suppliers, cost of goods, liability etc.). These requirements can be at odds with performance.
That being said; I hope that they introduce an excellent product and I wish them every success.