A little bit, yeah. I thought you were talking about the monarch’s personal domain, i.e. the crown lands he hadn’t granted away, my fault.
Yes, land ownership ultimately vested in the king but in the process of granting it away to tenants in chief the king also surrendered a lot of associated rights. This was a practical matter, medieval kings didn’t have the effective power to rule over even somewhere the size of England with delegating authority to the barons, but because feudalism was essentially contractual it was also a legal matter as well. The question of whether the king was constrained by law or could act as he pleased had been thought of and codified before Magna Carta.
Unfortunately my sources from the last time this subject came up here have suffered linkrot but this is a good thread on the myth/reality of Magna Carta. Key points for me are:
Similar limitations to regal power were being codified in Spain and Hungary contemporaeously a little earlier.
English legal documents from 100 years prior make reference to the accepted limitations onthe king’s power, including in areas such as right to judgement which crop up in Magna Carta.
Legal scholars in the previous century were writing about the well understood limits on regal power.
The point of Magna Carta was that it was firming up existing limitations which John had tried to ignore, not that it was introducing new concepts.
On this specifically, King’s habitually issued charters at the beginning of their reign, which included acknowledgement of the limitations of their power
The Magna Carta. - Great Debates - Straight Dope Message Board
Actually, I found the two Lord Sumption - Supreme Court Justice and medieval historian - that lay out this case best and cites an earlier regal charter.
Lord Sumption gives the Opening Address at the Franco-British Council Conference