Maybe the last couple of years have made me too skeptical, but I think there are a few factors that actually speak against a quick rebuild.
1. The prices in the transfer market. We can't go out and buy half a team in one transfer window anymore with teams like West Ham wanting 100M+ for their best players, they are totally within their rights to evaluate their players this way, but it makes buying half a team for top teams way more difficult, which we need to be aware of.
2. ETH isn't the guaranteed success a lot of people are making him out to be. I'm firmly on board with those saying that ETH currently is our best option, our best chance of getting back to success but is he guaranteed to succeed, I don't think he is, he'll have a fight on his hand, apart from adapting to managing in another league he will have to form a unit out of the players we still have and build a structure that can help us improve players again, if you ask me that's a monumental task with the way the team looks right now, and will probably require not only sorting out half of your player personal but also modernizing our training staff and methods over the next years. It also probably isn't only the training staff that needs overhauling, but also the scouting team and probably large portions of the rest of the staff, no department should be exempt from scrutiny.
3. Our owners and board haven't changed. If my work experience has taught me anything, it's that corporations who are dysfunctional usually are this way because the top level is doing something really wrong, may it be setting the wrong tone for the corporate culture, not delegating enough, being too controlling or due to gut feeling just overwriting decision way more knowledgeable people have made for good reason.
So yeah, I think this rebuild is going to be a monumental task and can only succeed if Murtough and ETH are on the same page on how to bring success back to our club and if the board stays out of it completely.