Western Light tanks go too fast in Era 1. It makes them toxic. They seem to have the historic top speed stock. THEN they get an even faster imaginary speed with the engine upgrade. Plus Turbocharger equipment adds an addition 5% on top of the already boosted speed.
Examples:
FV107 historic is 80.5. That is what is gets stock. But then with an upgrade it gets 86.9. Of course the FV107 is also from the Era 2 timeline, but a time machine put it in Era 1.
The Walker Bulldog 72 stock and historic but 80 upgraded.
RU 251 is 80 historic. Website is showing 89.3 both stock and upgraded.
The extra top speed they get is problem because it ends up making them toxic. They simply can outrun everything. They can stay ahead of guns and turret rotation. Add some internet lag or old gen graphics and they are quite difficult for the average player to hit. Lower than average players just get farmed even harder than they normally do.