It takes practice. However, in any multiclass league/series, or multiclass event these are the rules being used in, well, I can't say all, as I don't know that, but the wast majority. It is the faster class that has to pass safely. It's really frustrating when you catch a slower class car in an area where it is hard, or impossible to pass (right before Eau Rouge, so you have to slow down for Eau Rouge), Pouhon, Blanchimont etc. That's the part of multiclass racing though.
For cars with much more downforce, it's often smarter to do the undercut, as low/no-downforce cars will drift outwards. Same goes for modern prototypes and modern GT car. The prototypes are way more agile and have much more grip, so it's those who needs to consider this when passing. When a GT car has entered a corner, especially faster ones, it's much harder to change your mind midway to make changes. Now, I don't know how the GT-Vette behaved, but if I were to brake hard mid corner due to a Gr.C car deciding to lap me on the outside, then I would either lock up the fronts and go straight, or get so much front grip that I would spin. First lap at Eau Rouge on my stream (at 30:45) shows what happens with brake and turning at the same time in the Porsche.
Yet again, it's all down to practice and experience, but the reasons why this is
the rule for blue flags in multiclass is because it is the easier way from the different cars, but when people know this, it is much easier to handle, as you don't get one driver jumping out of the way, one going slow on the inside, the next going slow on the outside and the fourth driving normally.
I do think the ghosting of cars in Practice Session in AMS2 makes it harder as well, I noticed that Gr.C cars often drove through me during practice. If that wouldn't happen, people wouldn't have the first experience with this in the actual race.
I am also very much aware of me having done 3 seasons of RDLMS, seasons of other Virtual Le Mans series and have hosted 60-70 multiclass events in rF2 since 2020 do have a
lot of experience with this kind of racing, and thus look at it as very natural and logical