Flash bulbs need time to reach full output.
So bulbs need to be ignited some time before the shutter starts opening. That's what the FP contact does.
FP type bulbs burn long enough, and with near constant output, for the slit of the "F"ocal "P"lane shutter to travel across the film gate. Hence they can be used at all shutterspeeds.
X is for electronic flash.
Electronic flash 'burns' for a very short time. So the shutter needs to be fully open when the flash is triggered, or else some parts are lit by the flash, while others are not. That limits the fastest usable shutter speed to the fastest speed that still fully uncovers the film.
Electronic flash also reaches full output level the moment it is triggered. So it needs to be triggered when the first curtain has cleared the film gate completely, but before the second shutter curtain starts covering the film gate again.
So both the moment the flash is triggered and the speeds at with you can use either type of flash (and flash contact) are different.
P.S.
Olympus also made an electronic flash unit that, instead of releasing all of it's 'power' the moment the unit is triggered, fires in a series of pulses, that keep the flash's output at (or near enough) the same level for much longer.
With such a unit, you can use all shutterspeeds, not just the X-synch, just like you would using FP flashbulbs.
This flash unit could only be used with the OM 4 Ti (and 3 Ti?)
FP bulbs (and the FP electronic flash unit) should be regarded as continuous light sources (because they are). The aperture you use when using these depends on the shutterspeed you select (and vice versa). Not just on the distance and the flash's output.
Using regular electronic flash units, the flash duration is usually much shorter than the shutterspeed, and only the aperture has an effect on exposure.