Well, you may consider those good reasons for choosing the FTSE250, but that fact is that the 250 was never the basis for HYP, so as a comparator for HYP1 it's the wrong index.
So you consider the FT100 to be a good choice of benchmark? A better choice than others?
HYP1 and TJH HYP tilt towards smaller cap. Any time you move away from market cap you weight the largest stocks less. How that tilt away from size is performed - what and how stocks are selected is irrelevant when looking at it from a size factors angle. Look at the broader trend lines since the mid 1980's and FT250 and TJH HYP overlap each other, near-as the same. FT100 aligns (parallelism) more with All-World - and both were distinctly different to both the FT250 and HYP.
Of course, we can all choose whatever benchmark we like, depending what we are trying to establish, but as regards HYP1 and TJH, there can be little doubt that the FTSE 250 is not the correct one. People should be aware of that. In the end it makes little diffference except informs one's own agenda.
The FT100 is hardly a good choice of benchmark for HYP, not even a apples/pears comparison and more like apples/lemons, but each to their own. To clarify, I have no hidden agenda, unlike some that might look to promote/sell newsletters/whatever. Standard practice for comparisons includes measuring/comparing total returns, yet over 19 years of history HYP1 hasn't recorded such comparisons at all, on the basis of 'ignore capital' type policy and seemingly intentionally directing away from those that advocate Total Return type metrics.
If a real world portfolio tracks its mathematical index broadly then that is clearly a reasonable choice of benchmark. If the differences are large then the validity of the choice of benchmark is questionable. The clear indications are that the FT250 is a vastly better choice of benchmark for HYP than is the FT100. But yes even the FT250 isn't the best choice, a more equal weighted sectors index would be the better choice - but as far as I am aware there is no such benchmark index available.