But then again RTD wrote the Tenth Doctor as a vindictive superior a-hole who could only really be reigned in by a pretty bottle blonde
Somewhat (or vastly..) simplified, but yeah. 10 had the Timelord arrogance/potential megalomania boiling under the surface from the beginning. He believed in the human race having a huge potential for good, but it conflicted with his darker side.
He thoughtthat without a companion all the death and pain experienced by those he got close to could be avoided. That was a pretty big theme that was expanded on from School Reunion onwards, along with the Doctor's immortality against a human's tiny span of life.
Instead of some kind of peace, the Doctor's solitary travels lead to these elements beginning to overwhelm him, leading to the events of Waters of Mars, where he lost control his Messiah complex, then tried to run from it.
By the end he had come to fight with the feelings of not only the Doctor being the ultimate force in the galaxy, but his current incarnation being superior to all the others, hence his terror of 'death'.
His little rant at Wilf was that character coming to the fore for the last time before he conquered it, saving Wilf and accepting his need to change into something else.
You make not like the journey that RTD took the Doctor on, butting putting it down to bad writing is, I think, wrong. Davies' shortcomings as a writer lie in poor and repetitive plotting, bad gags and personal agenda. In terms of character, 10 went to places we've never seen the Doctor go before, and I think he was largeley successful in that aim.