I've been looking in to the Welsh nobility recently and the sheer number of titles that are often translated as meaning "king/prince/sovereign/ruler/lord/noble/chief" is boggling. I was wondering if the medieval Welsh had a sense of some being more prestigious or higher than others. I don't expect it to be as clear cut as, for example, England's Baron<Earl<Duke<King hierarchy since Wales was a mish-mash of competing realms of different levels of power and influence, but at least some sense of order would be nice. Was there the understanding that some should naturally be subservient to others?
For example, the Mabinogion gives the the title "Pendeuic" (modern Welsh "pendefig") to Pwyll and states he is "arglwydd" of the seven cantrefs of Dyfed. "Arglwydd" I take to mean lord in a general sense, that's simple enough, but where does "Pendeuic" fit in? It's usually translated as prince but then so is "tywysog", was one considered more prestigious than the other? The same apples to titles translated as king, teyrn and brenin, why two titles, is one greater than the other?
Then, of course, there's whether rulers are called king or prince. King seems more popular earlier with prince more popular later. For example, Gruffydd ap Llywelyn is given the title "King of Wales" but the later Llywelyn ap Gruffydd is called "Prince of Wales". Why is the difference, did prince become preferred because it was considered more prestigous than king?
Looking at medieval welsh rulers it seems random whether they are called pendefig or tywysog or brenin or teyrn. Also, they all seem to be pretty independent, would a minor local lord under another lord have a different title? Please help me make head or tails of this mess.
Welsh history is a bit outside of my wheelhouse, but titles of nobility are one of my particular interests. Given your familiarity with the period, I'd recommend looking at my secondary sources since they go into greater detail.
The answer to whether Welsh titles had a hierarchy is yes, but it's complicated. The issue at hand is that at any given time, there would have been a number of Welsh kings/princes (going by titles like tywysog, brenin, and rhi). We know that some of these kings would have been subordinate or lesser in status to others, but it is often difficult to reconstruct their exact relations to one another. A rhi would likely have been subordinate or inferior to a brenin, either having been granted portion of the brenin's land or inheriting a peripheral kingdom to the main kingdom. An example given by T. M. Charles-Edwards is that of King Gruffudd ab Owain, who likely ruled land in Gwyr that was part of the larger kingdom of Glywysing ruled by his brother, Morgan ab Owain.
The rather blurry historical record regarding these kings and sub-kings and their respective successions makes it particularly difficult to reconstruct their relationships into something like the vassalage of the Normans. Charles-Edwards argues that while we know that Gruffudd ap Llewelyn was the king of Gwynedd, we do not really know whether the kingdoms between the Wye and Severn would have been considered subordinate to his subordinate of Powys.
The transition to king to prince was likely part of the larger attempts to form political unity in Wales. J. Beverley Smith links the initial transition in title to a direct attempt by Owain Gwynedd to claim overlordship of Wales.
It seems rather that Owain made the change of his own volition in a period of strength, with a view to presenting himself as leader of his nation. In so far as the evidence of the letters may guide us, it appears that Owain did not cease to be king of Gwynedd in order to be prince of Gwynedd, but that he chose to present himself as ‘prince of the Welsh’ (princeps Wallensium). In his hour of triumph, with Henry foiled in his attempt to bring Wales into subjection by force, Owain projected himself as the focus of a broader unity. Becket did not miss the significance of the change and, evidently disinclined to reciprocate, preferred to continue to address the ruler of Gwynedd as ‘king’ rather than as ‘prince’.
The framing of prince as the overlord of Wales was further reinforced in the 1267 Treaty of Montgomery, which recognized Llywelyn ap Gruffudd as the Prince of Wales to whom the "barons" of Wales would pay homage.
Sources:
Carpenter, David. "Confederation Not Domination: Welsh Political Culture in the Age of Gwynedd Imperialism." In Wales and the Welsh in the Middle Ages, edited by Griffiths R. A. and Schofield P. R., 20-28. University of Wales Press, 2011.
Charles-Edwards, T. M."Dynastic Succession in Early Medieval Wales." In Wales and the Welsh in the Middle Ages, edited by Griffiths R. A. and Schofield P. R., 20-28. University of Wales Press, 2011.
Fisher, Deborah. Royal Wales. Cardiff: University of Wales Press, 2010.
Smith, J. Beverley. Llewelyn Ap Gruffudd: Prince of Wales. Cardiff: University of Wales Press, 1998.
N.B.
This is a slight tangent, but since you mentioned the hierarchy of the English peerage, it's worth noting that their system was also undergoing some flux during this period. Prior to the Norman Conquest, earl was arguably closer to duke. Earls were the highest rank of nobility under the king, and were rendered in Latin as dux. Earls only became comes (count) after a certain Duke of Normandy crossed the channel and presumably took issue with the idea of his vassals claiming to be his equals. The title of Duke wouldn't reenter the English peerage until 1337 under Edward III. At this point, Edward had just lost the Duchy of Normandy and pressed his claim on the French throne, making the issue of dukes imagining themselves the equal of the king a bit of a moot point.
Source:
Crouch, David. The English Aristocracy 1070-1272: A Social Transformation. New Haven: Yale University Press, 2011.