trials are not like you see on TV where Perry Mason always had the aha moment. Discovery and within that, depositions, generally remove the aha moments.

Once had heard a lawyer say: you never ask a question in court you do not already have the answer to.

part of the prep is finding those answers before trial.

with that said, it would appear IRLJ 3.1(b) states:

(b) Discovery. Upon written demand of the defendant at least 14 days before
a contested hearing, filed with the court and served on the office of the
prosecuting authority assigned to the court in which the infraction is filed,
the plaintiff's lawyer shall at least 7 days before the hearing provide the
defendant or the defendant's lawyer with a copy of the citing officer's sworn
statement and with the names of any witnesses not identified in the citing
officer's sworn statement. If the prosecuting authority provides the citing
officer's sworn statement less than 7 days before the hearing but not later
than one day before the hearing, the citing officer's sworn statement shall be
suppressed only upon a showing of prejudice in the presentation of the
defendant's case. If the prosecuting authority, without reasonable excuse or
justification, fails to provide the citing officer's sworn statement, the
statement shall be suppressed. No other discovery shall be required. Neither
party is precluded from investigating the case, and neither party shall impede
another party's investigation. A request for discovery pursuant to this section
shall be filed on a separate pleading
.

unless your request for discovery was late, I do not see the prosecution as having the right to refuse your request. Along with that, I do not see this section giving the prosecution any specific rights at all. It does limit what information can be sought under discovery based on this section though.
what was their claim for not being required to act as this section directs?

this is the only thing close to a right afforded the plaintiff by this section:

Neither
party is precluded from investigating the case, and neither party shall impede
another party's investigation
you shall not impede another party's investigation. That's it. I see nothing that directs the defendant to provide and information regarding their witnesses testimony.