Since you named his trueborn son John/János, I'll take that he was born before his OTL half-brother (pre-1473).
The prospects for Hungary are definitely good, but not great. True fact, Mathias was a great ruler, but his rule wasn't really sustainable and relied too much on a overcompetent and charismatic king like him. The death kneel of the governance was his revenue, to maintain the Black Army it's estimated to range something from 400,000 to 650,000 florings yearly, in the most opportune situations (good harvest/mining, two exceptional levies in a single year) the annual revenue of 600,000 florins (the Ottoman revenue was around 1,500,000 btw), so Mathias relied heavily on warfare and overtaxing the nobility to keep his Elite Mooks, it's simply set to blow on John's face (succession, even if crowned on his father's life, isn't often a smooth affair).
Another issue is that even if Mathias curbed the Estate's power during his lifetime, that doesn't means that they can't rise again (see Sigismund) and putting a choke on the nobles' neck is going to be painful. So in sorts, a part of Mathias' work is going to be undone unless you want a civil war (probably with Frederick and Maximilian screwing you up), but simply avoiding the Corvinus-Habsburg-Jagiellon tango and Vladislav destroying Mathias's life work completely and setting Hungary back to Albert-tier mess is going to benefits Hungary in short and long term (hence "good, but not great").