Originally posted by Masamune
Imagawa starts with a four-star and his first heir is also a four-star, but other than that they only get one other four-star later in the game.
The second heir of Imagawa is Ieyasu (later Tokugawa in RL) that is a 6 star - as opposed with the incompetent son of Yoshimoto, Ujizane, who ended up his days as a noble in Kyoto, having lost his lands and clan after his father's defeat and death in the Battle of Okehazama, solely living out his days to their natural end due to the kindness of Ieyasu.

...but I think it's reasonable to say that the number of high-star generals a player has at his command has a significant impact on game difficulty, and some clans are more fortunate in the leadership department than others.
Indeed - the clan with the best leadership is - as it was historically - the Takeda. There are however a few historical innacuracies, regarding generals that historically belonged or lead different clans to STW clans solely because of their geographical proximity/association; ie because their clan could not be represented they appear as part of the clan that occupies their territory.

For example Hiraga Genshin that appears as a general for the Takeda in 1530, was one of the Takeda rivals in Shinano and was defeated by a 15 year old Takeda Harunobu later to be known as Shingen. Other examples include Asakura clan leaders/generals apearing as Oda retainers or Satake leaders/generals appearing as Hojo(?) retainers etc.