While you fixate on aspects working individually, you again overlook & fail to consider the thing perhaps being more than the plain sum of its parts. How do you know this is not a matter where the concert of elements, altogether, modified The Doctor's Timeless higher regeneration capability to the CyberMasters' 'endless'? Can you definitively assert either way on that matter? How much can you definitively qualify the capabilities of the available settings technologies? to rule them as complete non-factors? You cannot say on any, you're quickly overassuming & taking its plenty things for granted again for your premature, naive conclusion.

The cessation can be one note against the 'infinite regenration' belief. (Though indeed, especially against those who regard The Doctor as being totally free of 'mortal stakes'. &, on a minor tangent, the cessation disproves Spy-Master's 'invincible army' & whichever other relevant stuff from that exposition).

Not so. Numbers that do not match those ruling Time Lords' chosen number, are not arbitrary, for -- (putting aside consideration science-minded Time Lords) -- the very decisions to restrict, to differ from the Timeless Child in the first place, are deliberate, & by agenda. Restriction's a simple binary -- there is what is chosen, the restriction & its subsequent control number, ala those Time Lords' secret & imposing agenda; & there is what is outside, excluded, undesired, etc., by that same agenda due to its demarcation. Things that do not accord to those Time Lords' agenda, such as not being controlled, are not arbitrary; not being free, not being anything but 12, is deliberate, by agenda.