Exactly. That's why I'd never be able to implement my single engine formula. It's not that equivalency formulas don't necessarily work, but it's very hard to be objective about if they're working or not when there are so many bikes to take account of. It would be much simpler if the equivalency formula wasn't needed. It's not as though Ducati can't make a four - they made the Desmo RR.
In the top levels they are a necessary "evil", the specification of "Item 1. Must not exceed 600 kgs total weight. End." is no longer considered an acceptable rule book in motorsport since 90-100 years ago.
We see two main schools of thought for producing close racing and even playing field.
1. Technical parity. The cars will perform the same or similar because they are the same. This is the model, of course, used by NASCAR. The chassis are identical and the four different engines are all-but identical in specification. This is also the model used by F1, not quite as strict but not far off. Your 2.4 L V8 must have this many valves, this stroke, this bore, this COG and be made of this material. You must use these tyres. You must use this ECU. And so forth. It is also the model used by DTM, where all cars will be based on the same Dallara chassis. Furthermore, the Aussie V8 and the Brazil stock car series have the same thinking. Not to mention the countless spec series (from junior formulae to sportscar series like Carrera Cup and Ginetta racing) that cater to professional and amateur racers (and F1 technical directors

2. Performance parity. Cars prepared equally well and driven equally well should have the same chance of a result, even though they different technical specification. Some balancing measures are applied, either beforehand or on an ongoing basis throughout the season. This is, of course, the model used by the ACO at Le Mans where petrol, diesel and hybrid vehicles are supposed to fairly balanced by a series of measures including the engines themselves as well as different fuel tank allowances. For years the provision for 1500cc with forced induction went unused within the F1 regulations, until it became the better choice. MotoGP has traditionally been closer to allowing freedom, but will create their own performance parity situation with the introduction of the claiming rule bikes within the MotoGP competition.
A couple of poll questions:
1. Which do you prefer as a racing fan or competitor?
2. As an F1 focussed bulletin board, which would be the better direction for F1?