Conversation so far:
What kind of artist was Matthew Paris?
Matthew Paris was artist in illuminated manuscripts.
Did Matthew Paris do a lot of drawings?
Matthew Paris wrote a number of works, mostly historical, which he scribed and illuminated himself typically in drawings partly coloured with watercolour washes, sometimes called tinted drawings.
Did Matthew Paris influence other artists?
A strong influence Matthew Paris' style was the Carolingian Utrecht Psalter. This was copied in the 1020s in the Harley Psalter, and in the mid-12th century Eadwine Psalter.

Question: Why did he feel that way?
Self-contained rewrite: Why did Nigel Morgan feel that Matthew Paris' influence on other artists of the period has been exaggerated?