As for the matter of How useful the ToC is, well, it's useful. But a lot of its use comes from analyzing average placements over a length of time, and elaborating on why a certain series is ranking in a certain way (i.e. is a series like Chainsaw Man ranking low because of it not being popular with the readers despite great upwards trend in sales, or is it ranking low because of Shueisha playing it safe in regards to its violence and NSFW content? By all means, the most logic conclusion would be the latter, in a similar fashion as to why ecchii series are placed at the bottom).
The only metrics that can without a doubt measure popularity of a series are sales and questionnaires, but we do not have access to the latter; either way, the ToC is usually a balance of the two. It is no coincidence that the first newbie to rank truly well in quite a while, Mashle, was also the one to have the best debut by quite a margin in terms of sales; Shueisha obviously has some info on how liked the series is within the readers of the magazine beyond just how much a series sells. Bottom rankers tend for the most part to be flops, but series that hang around in the upper half in a consistent way usually end up performing.
What ranks high and what doesn't is fruit of editorial decisions, however these decisions aren't made out of thin air; if something is being pushed, then someone must think the content warrants pushing. It could simply be due to the series being a sales juggernaut, or it could also be due to questionnaires leading the editorial to believe that the series has potential to become one. It's no coincidence that veterans that aren't performing anymore tend to be moved to the bottom of the magazine, with the series being removed from the lineup relatively shortly after.
In any case, with the current state of the magazine, I wouldn't expect any newbie to just sit at the bottom forever, or at the very least not until we move closer to the next serialization round.
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