Unless you are talking only about competing in terms of having the games still being competitive late, then it's not a ridiculous timeline at all. When people are talking about scrimmage seasons, throwaway seasons, rebuilding years etc, it is referring to competing for things like divisional/conference championships, not individual games. And no, it isn't a ridiculous timeline to say it's going to be 3 or 4 years before that can happen.
When Collins took over he inherited an OL that was recruited for and coached to a very different system; one which largely ignored a fundamental part of the offense we want to run. He also inherited a bunch of QB recruited for that system who's strengths didn't align with what we need. There were no TEs, and a WR group that was largely unproven. On the other side the defense had largely been a big weakness for a decade and there were legit concerns about the front 7 not just in terms of coaching, but in terms of whether there were the pieces there to have success.
The truth that many didn't want to accept last year, and seems many still don't want to this year, is that some of the issues that we had were almost certainly going to have to be addressed through recruiting and developing those players. But if it takes bringing in new players and developing those players to fix those issues then looking at year 4 or year 5 makes sense. In year 4, the first real class of a new staff, meaning not the transition class, will be either true juniors or redshirt sophomores.