If he said that then his point would have been vulnerable to the fact that we've seen summoning used for combat a lot more than we've seen it used for anything else (tracking and reconnaissance being the only other uses I can recall).
By writing that giant brick of text he creates a point that can be disagreed with but can't really be called 'wrong' since it's an expression of personal interpretations instead of a simple declaration of 'facts'. If anyone deigns to disagree he can point to the instances where he uses the word 'assumption' so that he can't be called wrong.
Personal favorite line:
I've noticed explanations seem to be 'obvious' to Abdula if there is any reasonable evidence that they are correct. And since these explanations are 'obvious' any 'assumption' made that would assert those explanations are not the correct explanations for the events which they explain must be illogical and therefore foolish.Jiraiya didn't use Gamabunta and again I'm just assuming because he obviously felt that if it just came down to a battle of summons Pein would win.