The strength of a summoned phantom beast was comparatively different than a contracted magical beast. The strength of the summoner would determine the power of the phantom beast.
The phantom beast was also more fearless because of the strength of its summoner. Furthermore, one could only be contracted to one magical beast in one's lifetime, but a summoner could gather several creatures if they were powerful enough to summon them at the same time.
That was the reason the masses dreaded the warlocks. It was not because they could not defend against their curses effectively, but rather it was because the warlocks could summon extremely powerful creatures to keep their enemies at bay.
