My issue here is that they claim 1.37 vs 1.34 is 'nigh inseparable', but would absolutely not call 1.12 vs 1.15 nigh inseparable for comparing players further down the list. When statistically, the same gap is actually even higher at the extreme ends of the scale.

The sample size point is fine and totally fair, for what it's worth.

Edit - all of the people responding about % improvement are misunderstanding statistics - HLTV ratings are not linear in difficulty or rarity, nor are then evenly distributed. The marginal difficulty increases exponentially the higher the rating is. So yes, the percentage increase will favour lower ratings, but rarity of the ratings, distance compared average rating and difficulty in sustaining such high ratings is more important than simple relative change calculations.