Jamie himself is not an issue, I don't see the issue with the GA team being individuals itself, as you allude to Jamie does fit that particular bill from his time in Northern so would have good experience there.
The number two, also the project director was also a bid director in the past and a business development director, Operations director was previously head of business development, for me it's a little bit samey and ideally in my book at least, you'd want a mix of skills, so if a MD had great engineering skills and operational skills, you'd want a deputy or a senior director who had commercial and accountancy skills.
The lack of a real operational or engineering or fleet transformation expertise in the senior leadership team is not ideal, but if you had a real strong railwayman as an engineering director with a lot of input it wouldn't be so much of an issue, but if you add to that an engineering director who is relatively new to the industry, then that has to be a worry.
With that being the case it would be prudent for Abellio to somewhat involve a senior member of the engineering team who is not a director, in the project team alongside the ED, especially if said team member has experience in rolling out new rolling stock, since their experience would be valuable, since however good the ED is, experience in a project this size is going to be valuable.
Personally I'd have went out and got a good experienced ED if I didn't have a senior leadership director with such experience for such a project though, because like you say, Abellio will live and die by how this goes and if it does go wrong it could go spectacularly wrong.