A large quantity of Merlin's workforce in front-line roles like this are youngsters in college or university, some of them with it being their first proper customer-facing role. It's true, you do need a thick skin to cope in such roles but when it's their first, having that thick skin isn't always possible as it needs to be developed and adapted as they encounter each different guest concern.
When you have the full control of a ride all by yourself, under pressure to be as amicable with guests as possible yet working under the stress of having to keep queues short, it can get hideously overwhelming. Having that second person by you not only mitigates those stresses, but also helps to keep control in situations when a guest takes advantage of you being by yourself when they get arsey, verbally, or even physically abusive.
There is no comprehensive training that Merlin has in place to deal with guest situations if you're a ride operator or host. Particularly on some of the smaller rides across the group, where you won't need as many hours to be signed off to work it by yourself, there is every chance that you don't receive sufficient exposure to the dark side of the general public before going solo. There's then every possibility on your first outing operating as an individual, you can be put under extreme pressure or face the nastiest of guests without any confidence in having reinforcement; especially when managers hide in their back offices or pretend to look busy with a litter picker elsewhere.
The lack of staff training in dealing with difficult guests and de-escalating conflict is a problem. As you say, it’s a problem because for a lot of staff it’s their first job, and they may not have much experience with it. It’s also a problem because it means that staff don’t know whether the managers are going to support them. When there is no procedure for dealing with conflict, it’s easy for managers to place blame into the staff member with comments like, “It takes two to tango”, “It sounds like it could have been handled better”, and “You must have said something to make them so angry” etc If there’s clear guidance of what to say and when security or a manager should be called, it helps to cover staff members from being told that they dealt with it wrongly.
I do think victim blaming is in Merlin’s culture, where the victims of abuse and assaults are made out to be too thin skinned, or lacking the skills to deal with conflict. Over the years Merlin have cut back on the number of managers and security to save money. This means staff are perhaps under greater pressure not to escalate issues and call for assistance.
One upshot of this is that a lot of abuse and minor assaults are never reported. This is particularly true if staff members are looking for a promotion and know that calling a manager/security will be seen as a sign of weakness. If issues aren’t reported, it might well mean that a group of thugs are able to assault multiple members of staff, which certainly has happened at Merlin parks.
It is also true that there’s a big difference between running a flat ride on your own when there’s not much of a queue, and running one on your own with a 45 minute queue, which is clearly going to be a lot more stressful. If a child is too short, they’re also likely to be a lot angrier if they’d been queuing 45 minutes compared to if they’d just rocked up.
One suspects that staff are a lot more likely to take abuse and assaults in a park with lots of one and two star reviews on Trip Advisor than at a highly rated park like Europa Park. Again, I think Merlin are often keen to present any abuse or assaults as isolated incidents, and while to an extent they are, they are also a symptom of a park with a lot of angry customers.
Of course, some customers will be rude and you have to have some thickness in your skin, but it’s not unreasonable to expect an employer to take reasonable steps to protect their employees from abuse and assaults. Remember, ride operators aren't paid danger money. They're paid the minimum wage.