But this shouldn't mean you get the right to flood the court with obviously frivolous "motions", each requiring days / weeks of back and forth between prosecutors, defenders and the judge.

Yes, it does.

This may seem like it's unusual for folks who don't ever get much of a peak into pre-trial motion practice. But it's not. There's a reason why many criminal cases can take many months, and sometimes years, from indictment to get to trial. It's because there's commonly lots of disputes between the state and the defendants over a host of issues, from process to discovery to admissibility of evidence to disputed points of law. All of those things have to get sorted out by the judge. To use some famous examples, Elizabeth Holmes was initially indicted in 2018, there was a superseding indictment in July 2020, and her trial didn't start until August 2021. Martha Stewart's indictment was issued in June of 2003, and she didn't go to trial until March of the following year. Ken Lay (of Enron) was indicted in July 2004, and didn't go on trial until January 2006.

These are perfectly ordinary and common things for defendants who are represented by counsel to ask for. They will file motions asking for every possible procedural and substantive choice by the judge be made most favorably for their client. That doesn't mean that they'll get everything they ask for, of course. But there's nothing wrong, or even that uncommon, in them filing all these motions - and it doesn't mean they're frivolous. In fact, unlike the sometimes petty disputes that can arise in litigation, questions about the timing and co-defendants in a trial can have a huge impact on the outcome - so it's both natural and appropriate that there's a flurry of early pre-trial activity on that issue.