I think a lot of people are going to be surprised by how much difference a top class manager, backed by a top class coaching staff makes. Assuming that is what we do of course. All the candidates has shown themselves capable of changing their tactical plan on the fly in response to the opposition, something we haven't had since 2016-2017. That in itself will help with results. The majority of games we've drawn and/or lost since Ralf's appointment has been because we have been incapable of meeting tactical changes the opposition makes. There are so many points wasted on that this season, if you take away those we easily make top four, likely progress in the CL and begin competing for top three - despite having a sub-optimal squad with a weak midfield.
Since Ten Hag is favorite to land the job, it should be pointed out that he in particular has an incredible statistic when it comes to creating a system that works with the players at his disposal - Ajax has scored 80 goals in 27 matches, conceding just 13. That is astounding no matter how you look at it. He has like a 74% win rate over his time at Ajax, which is borderline unreal. Add his time at Utrecht and you're still looking at 64/65%. Clearly he knows how to get a squad playing to the limits of their abilities - hopefully that translates when he starts working with "bigger" stars and a much bigger budget (Ajax eecord transfer is £25M for Onana IIRC)
We will probably still buy players for silly money for marketing reasons, but as long as we follow through on hiring world class coaches and let him develop his system we should be seeing considerable progress made within a relatively short time span. Ralf has done quite a bit with our positioning, chance creation and players adhering to a system in a short amount of time - he and his staff are just awful at making the necessary changes during matches to get the results as well, or simply bad coaching (set pieces, finishing, composure). Ten Hag does not suffer from that deficiency, so there is no reason to believe he can't get similar improvements both in team performance and results rather quickly. Provided he gets players and coaches capable of implementing his preferred system.
Personally I think the same is true for all three leading candidates, so all in all I think there is certainly room for optimism at this point.