Ok, this will be a long answer for a long question.

Strategic consulting and most Fortune 500 companies operate at very different speeds, and moving from consulting to the industry will be shocking, at least in the beginning. The industry feels slow, and not assertive, decisions take way longer to be taken, most of the times there is an unspoken desire to have a full agreement before taking tough decisions.

So, in my opinion, it is not a downgrade just change of scenarios, with a change in pace and career progression as well, on the other hand, there is up or out rules in the industry.

I find it hard for the industry to be as exciting as consulting, you will also miss the mind-blowing problem-solving sessions from consulting. In the industry, this is much slower and less important than in consulting.

If you do it right and build the rapport that a good internal consultant advisor should have, it can become very influential, and soon you will be the unofficial advisor for several leaders, but again remember, the industry moves slower and will take time and dedication to get there.

I hope you do not become a back office employee, otherwise your future is gone, you need to be ahead of the game, deliver what has not been asked, predict what will come next and be ready, become invaluable for the leadership.

It seriously depends on the firm. I work in corporate strategy at a very large EU media group and I can tell you, it's far from being a back office.

I believe there are a few perks - slightly better hours, interesting career growth possibilities (leading a business unit / entity for instance), usually seen as a central piece of the company (sometimes too much, and perceived as an Ivory Tower), very diverse range of tasks

At the end of the day, what you want for yourself is the most important part and that, I cannot answer for you. What do you value more and where do you want to be in a few years' time?

FYI, most high growth unicorns rarely have a strat team. They have a BD team and a few execs/ founders that are responsible for the vision and the strategy of the firm. Of course, it depends.

Your life will most probably be way less hectic, less travel, more time for yourself. Can you accept/enjoy that? Or do you need the adrenaline and the non-stop traveling? It also depends on how old you are. Below 30, you might want to stick to consulting and after that, depending on whether you see yourself as a potential senior partner or not, it might be time to make your exit and decide where you want to work, what you want to do in the future.