Ichigo's doesnt have any boost in strenght in BK. Its just that he can put more reiatsu in TZ blade than in Shikai. Its just normal thing in BK.
Also I think that Ichigo would still have problem if he used his super speed for to long. Afterall his speed is always boosted beyound what he himslef can do aka beyound his limit. So his body wont be able to withstand it forever
The three with the most potential are (in order):
I seriously think that Hitsugaya is the best bet for future Soutaichou, in the loooong run. Even if Ichigo and Zaraki have the strength required, they're both idiots and unsuited to leading. Plus Kenpachi fights for selfish reasons (which I personally have no problem with, but it makes him unsuitable for being the Soutaichou).
Dunno. However I do recall reading somewhere that he later one didn't use the super speed as much because of the bad experience earlier, or something...could've been even a forum post though.
im not sure about the most potential, but i imagine that yachiru must have a ton of latent potential, considering how young she was to be a lieutenant
we havent seen her fight at all really, but i imagine she is quite the bad-ass at this point
its debatable who has the most potential and strongest since kubo makes power levels so unbalanced or asspulls. its also about personal opinion. its already known that the more unpopular characters get shitted on/don't grow, and the more popular ones get power boost, ect. kubo keeps characters in the dark to long or misuses them, so its hard the gauge until kubo shows everyone's power.
Ichigo because of his blood-mixture and because he is the protagonist.
I agree. Kenpachi have potential due to just getting his shikai name after already being on captain level.
Ishida have potential too, due to the conversation Ichigo had with the quincy in HM.
I'll like to dominate Hitsugaya into the list too. It's obvious that his popularity and his training would give him rather nice power, regardless of Kubo original intention.