What you say is correct in principle, but ignores the important fact that practical car engines are horribly inefficient, and their effeciency changes quite a bit over the range of speed and power required to move the car. Note that this is the point of transmissions. At best they don't loose any power, but they make the overall process more efficient by allowing the gasoline engine to operate at a more efficient point.
In one way, you can look at a hybrid as having a wide-ranging finely adjustable transmission, but there's more to it than that. The efficiency of a gasoline engine is in part related to what fraction of peak power it must put out. If the gas engine is the only mechanical output in the car, then it must be sized to supply peak power. However, most of the time much less than peak power is needed, so the engine often runs at a inefficient point.
With a electric motor available to fill in the when peak power is demanded, the gas engine can be sized smaller and it is easier to make it more efficient over most of the normal operating range. It also allows for the option of not using the gas engine at all at very low power levels where it would be very inefficient. Instead it can effectively be run in bursts of more efficient operation. For example, if the gas engine is 3% efficient at 500 W, but 6% efficient at 1 kW, then you're better off running it at 1 kW half the time instead of at 500 W all the time. With a hybrid, you have this option. With just a gas engine, it's stuck having to produce whatever power is demanded at the moment, regardless of how efficient that is.
I have a Honda Civic hybrid, and I can tell you this stuff really works. I routinely get 50 miles/gallon minimum on the highway, often substantially more. The engine is physically small for the size car, and it has been specially designed to be easily shut down and restarted. Going down a hill, even at highway speeds, the engine often turns off. If the hill is steep enough, the motor is run as a generator and charges the battery. When I get to the bottom of the hill, I can see that for a little while the control system uses the electric motor to keep the car going at the set speed (this is all with cruise control engaged), then eventually gives up and switches on the gas engine. I can feel a slight klunk when that happens, and the charge indicator goes abruptly from discharge to charge.
Because, when you brake, your weight is being shifted towards the front wheel. The inertia coupled with gravity puts your weight and that of the bike onto the front wheel. More weight ⇒ more pressure ⇒ more friction/grip with the ground.
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The answer depends on whether the wheels skid.
When you brake with just the rear wheel, it's quite possible to skid; if you apply the front brake, the increase in normal force on that wheel tends to prevent skidding (although in extreme cases it could make you fly over the handlebars).
Applying the rear brakes hard enough to block the wheel would generate little wear of the brake system, and lots of wear on the back tires. The same thing would not happen at the front.
In practice, which brakes wear more really depends on how much you use them. For motorbikes, it is recommended that you use the front brake more heavily to prevent skidding - in fact some bikes have a mechanism that pretty much ensures this.
But from a pure physics perspective, the kinetic energy that needs to be dissipated is the same, regardless of what brake is applied.