Off the top of my head, more than adequate for mid-table in the top tier:
Terry, Chester, De Laet, Taylor, Jedinak, Lansbury, Hourihane, Grealish, Veretout, Kodjia.
That is a goalkeeper off a full team. I would add that in the right condition and with the right coaching we could also potentially count:
Johnson, Amavi, Bree, Baker, Lyden, Green, RHM as easily good enough.
Finally, We have the likes of McCormack and Bjarneson who we surely havent seen enough of to make a judgement on.. The others, the likes of Agbonlahor, Richards, Bacuna, Gardner, Hutton, Elphick have all had golden patches in their careers at one time or another. With a good preseason and the right condition, I wouldnt be surprised to see a renaisance from a couple of them. I dont think its as big a rebuild job as you think