I dont think it is unreasonable for the classics to get faster, Becaquse the bikes are getting faster.

The modern classics are not 50 years old you can bye a brand new one for godsake. They have modern fully adjustable front suspension. Good rear suspension, the mmcc even allowed adjustable master cylinders this year. The frames are made of tubing far better than in the period. The bikes are lighter they're covered in carbon, magnesium and titanium. Avon and dunlop now offer continually improving tyres in a variety of softer compounds and the top teams are more professinal than ever.

Most importantly the engines are getting faster and so is the circuit!