@bananasplitwithcherry raises very valid concerns and it is interesting that a similar impression was formed by one of @noblegiraffe's students. As @sendsummer says, an Open Day talk is only one imperfect 'data point' in an array of other imperfect data points.
The stakes are high for the current cohorts of students and HE threads here on Mumsnet often demonstrate that the experiences and benefits of attending uni have varied enormously and often for reasons outside students' direct control. Not all institutions or departments have necessarily made the best of a difficult few years and it is natural that applicants and parents are more sensitive to both hard evidence and softer impressions.
There have been previous threads about applicant and parental reactions to Open Day talks and these have exposed various tensions that exist within the current Open Day format - with its mix of academics who perhaps feel coerced into a 'hustings' style situation (as they sense a more critical atmosphere), uni marketing staff evaluated on how appealing they present their institution (and so prone to dialling up the 'promotion') and finally, of course, applicants and parents understandably anxious to decipher whether the website 'promises' hold any water.
Personally I think the Open Day format is in need of a fundamental reset, to the benefit of all parties involved. Open Days could return to being held mainly on weekdays (with colleges and schools told to drop their ban on weekday attendance), particularly in the early summer period after uni exams/A-L mocks.
The more structured side of Open Days (beloved by uni marketing depts if only for reasons of competitive escalation) could be dialled down to reduce pressures on all sides and allow programmes to start later in the day (and finish earlier) so students can make their own way to Open Days by public transport if that is their preference. Some talks and informal sessions with existing students might be strictly applicant only. Yes, we have train strikes currently but unis (and staff within unis) might be willing to run a larger number of weekday events if they are generally less intense in nature; that would inject some much needed flexibility. As it is, you have large numbers of unis homing in on the same Saturdays in June, Sep and Oct.
There does not have to be a complete switch from the current model of weekend only/heavy parental presence/lots of structured talks; I do understand why all those aspects can be useful, but the blind adherence to the current approach does need to be challenged. It sounds as though the Imperial Open Day Maths talk was one where no one benefited really and that is not a good outcome.