I think there is only one meaningfull criteria for becoming a FI. You have to genuinely like teaching. If you find teachng satisfying then you will enjoy your time as an instructor. If you do not then you will rapidly become frustrated and do yourself and your students a great disfavour.
Therefore I think it is a wonderfull thing that this pratt does not want to be an instructor, because with his attitude he would be terrible. I do not know how it works in the UK/EU but in North America 500 hrs flying scenic flights in a 172 will be looked on as 1 hr 500 tmes by most chief pilots. It would not be seen as any more usefull preparation for the next step, FO in a MULTI IFR airplane, than 500 hrs of instruction.
Finaly I would like to note that in my business, fire bombing, I think my extensive flight instrutor experience has served me well. It gave me good stick and rudder skills, a disciplined approach to flight operations and excellent comunications skills.
