I work in a related field and while I don't know anything about supercomputers being more realistic, there is a movement to eliminate animal testing and instead use organ-on-chip models - still using cells, but in vitro. The advantage is not only that you eliminate animal suffering, but also that you can use human cells, so your tests are much more quickly applicable to humans. In fact, in a far away future, you could even test with your cells and see how a specific treatment affects you. Super interesting stuff!

Computers can run a model...but you have to have real world data to create and improve the model. Plus there's always the chance the model is wrong or has some inaccuracy in it.