Yup it's all much later and there's little to suggest there way anything wrong with Warwick in early childhood or under Richard.
On the de la Pole's - the idea that Lincoln was Richard's heir is exaggeration and there is no hard evidence he was named as heir after the death of Richard's son - he was merely the only adult male relative Richard had.
You can hardly have him succeed in preference to his female cousin's when his claim rests on his living mother.
On Tudor - it is true that Margaret Beaufort lobbied Edward IV for her son's return (she was close to the royal family and wanted her son home in order to inherit her property) - there was no real formal invitation - his cause was regarded as a lost one and there was little Lancastrian support left. There was little incentive for Edward at this point to get him home - if Margaret died whilst her son was still in exile - her property could be appropriated by the crown.
In strict succession terms Richard's lawful heir under the normal standards of primogeniture would have been his niece Anne St Leger - if you accept the exclusion of Clarence's children and the daughters of Edward IV -
Richard III, Anne St Leger *daughter of Anne of York*, Elizabeth Duchess of Suffolk, John de la Pole, 1st Earl of Lincoln, Edward de la Pole , Edmund de la Pole, Humphrey de la Pole, William de la Pole, Richard de la Pole, Elizabeth de la Pole, Anne de la Pole, Catherine de la Pole, Margaret Duchess of Burgundy, issue of Isabel Countess of Essex (sister of Richard 3rd Duke of York)
As I said earlier the choice Edward faces is Elizabeth I, Edward V (the Earl of Warwick) or his brother Richard III - likeliest is he pushes for his daughter to succeed and arranges an early marriage for her with either a husband strong enough to defend her rights or high in the succession themselves - Warwick is nine years younger than Elizabeth but a match wouldn't be impossible if it secured the throne for the two of them for example - otherwise a strong foreign Prince of a better age. Edward IV was popular and might have been able to carry parliament to approve his daughter's rights as his heir.
Isn't the idea Clarence's son suffered a mental disability a mere rumour based on a single chronicler saying he "couldn't distinguish a goose from a capon"? Which is entirely understandable without Edward being disabled- of course a kid who has been imprisoned since he was 10 and denied an education and meaningful human contact is going to be a little off, but that doesn't mean he suffered some intrinsic mental incapacity.