Think people are exaggerating the long term plan, but the plan of mainly buying 22-25 year olds & trying to nurture & add to them to improve year on year is tried & tested, it's not exactly rocket science. If you can add in a sprinkling from the youth team that helps with the build as well.
Look at when Klopp took over, bought the likes of Robertson, Mane, Wijnaldum, Matip, improved the team first couple of years, managed to spend big money on the likes of Van Dijk & Allison to take them up another level. Trent, Gomez, Jones all coming through as kids as well.
Even Solskjaer has spoke about he was given 3 years to challenge, signed Wan Bissaka, Maguire, James, improved & steadied the team, Bruno improved them further which enabled them to go & get world class players like Varane & Ronaldo to try & get them to really challenge. The likes of Greenwood coming through to add to that.
Even Chelsea done similar under Lampard, adding the likes of Pulisic, Werner, Havertz, Chilwell over a couple of windows & bringing through Mount, James etc. However, they also decided on a change of manager to improve them. That has allowed them to spend big money on mostly Lukaku to try & springboard their challenge.
It's not exactly a vanity project, or a PR project like folk have claimed. Sometimes depending on the wealth or standing of the club its just done at different levels.