My understanding is he was NOTimportant in the development of armoured warfare in the inter war period, that he claimed credit for the work of others and that his book is factually incorrect (ie lies) but that English speakers have a high opinion of him because they do not critical engage his work and because of his service during ww2? Is this true?
Your understanding matches with mine (Granted, possibly because I have helped promulgate it in recent years).
Various authors have pointed out that statements by the Germans after the war are to be taken with a pinch of salt, such as Yeide's assessments of the German opinions of US General Patton at the time vs what they announced after the war to the Americans. After all, their futures were now basically in the hands of their former opposition.
I'm going to link you to two videos.
The first, commentary by David Fletcher of The Tank Museum, Bovington, and Hilary Doyle, probably the best living authority on German armor in the English-speaking world, if not actually the world, period.
This should be timestamped to about 7:45 in. https://www.youtube.com/watch?v=_oLY4FOrnjc&t=465s
The second is an interview with Ralf Raths, the director of the Panzermuseum in Munster, the German Army's official tank museum. Guderian's influence (or otherwise) is discussed at about 14:48. https://youtu.be/pFGZV-PDbWM?t=887
Ralf's position generally matches with Doyle's. Ralf states that his only notable input on the theory was to push the idea of radios being common. Being a signals background, this isn't surprising.
The people who had actual influence were folks like Lutz who were out of the picture before the war stated. Guderian had two pieces of good fortune. Firstly, he wrote "Achtung! Panzer!", which, contrary to a common perception, was not a dissertation by him on his opinion on how panzers were to fight, but was actually more of a primer piece that Lutz told him to write for the rest of the Army to understand how the panzertruppen had decided that they were going to fight, the decision on how had already been made. Unfortunately, his writing it resulted in the ideas being associated as "his".
The second was that, as you suggest, he was an excellent practitioner of armoured warfare. He may not have had much to do with thinking it up, but he certainly took to it. This inherently gave him credibility on the subject. He doubtless was well involved in the practicalities of training and implementation of doctrine, given his position at the time.
So, as Ralf says, 'He was a genius at making people believe he was the genius behind armor tactics.'
If you have a half-hour to spare, I go through who did what (more or less) here. https://www.youtube.com/watch?v=pbKAg4SRW_U