At the start of the 1430s, the York estates were supporting no less than three dowagers, the widows of Edmund of Langley, of Edward 'of Norwich' the second duke, and of Edmund, Earl of March. By the time York gained livery of his estates in May 1432 one of these ladies, Philippa Mohun, was already dead. The Countess of March passed over soon afterwards, and Joanne Holland in 1434, when York was still only 23.
There were some complications relating to lands that were enfeoffed, and there were also a few elements that the Crown managed to keep its sticky fingers upon, notably Duchess Philippa's Lordship of Wight. But nonetheless, the duke's income was higher than that of any other lay lord. His net income may be estimated at £5,800 a year. Only Buckingham (£5,020) and Warwick the Kingmaker (at his richest - £4,400) came close. **
It's worth pointing out that even this income was less than half that which John of Gaunt was enjoying in the 1390s. So when considering the topic of over-mighty subjects, it's clear that York was nothing like the threat to Henry VI that the Lancastrian set-up had been, potentially and actually, to Richard II.
The bulk of York's income was derived from the Mortimer (March) estates, the York (proper) inheritance coming next, with a further contribution from a sliver of what had been the Holland (Kent) properties inherited via York's grandmother, Alianore, Countess of March.
Landed incomes generally had been in decline since the Black Death, but a series of 'corporate mergers' meant that although there were fewer great lords than before, the families that suirvived were as rich, if not richer, than their predecessors. The Buckingham inheritance mentioned above was in effect a merger of the lands of Thomas of Woodstock, Duke of Gloucester with those of the former earls of Stafford and half the lands of the Bohun family, earls of Hereford in the 14th century. The Kingmaker's 'corporate history' was even more complex, including the Beauchamp, Despenser and Montagu (or Montacute) families to name but the three most lately 'gone out of business' as well as his father's meaty share of the Neville lands.
The poor relations were the Beauforts. Though they too enjoyed part of the Kent inheritance, the basis of their endowment was the relatively meagre provision John of Gaunt had bought for his eldest Beaufort son, plus a few bits and pieces granted by the Crown. Moreover, most of what there was had been left unentailed, which meant that when John, Duke of Somerset died in 1444 the lion's share went to his daughter, Margaret***. The succeeding Somersets, John's brother and nephews, were left with the proverbial pie's nest. This explains why they had to grapple so fiercely with York (and others) for influence at court and appointment to profitable offices. They had no choice.
** These figures taken from False, Fleeting, Perjur'd Clarence by M.A. Hicks.
*** Lady Margaret Beaufort, the much admired mother of Henry VII.