I feel like we should clarify what we are arguing about. Counterlooping and strong FH are not exactly the same. Counterlooping is more about timing and borrowing power from your opponent, so physically weaker players can be good at counterlooping, like Lin Gaoyuan and Harimoto.
I think players with truly strong FH can consistently create powerful opening shots with their FH. My reasoning is that in the initial attack, the attacker must supply most of the power and spin.
Ma Long's forehand is good. Among the CNT, Ma Long is more known for his counterlooping ability than for his power. So by my standard, Ma Long does not have the strongest FH.
In terms of pure power and spin, I think XX's FH is probably superior to Ma Long. However, I think FZD's FH is probably the most powerful. To prove my point, just watch any of FZD's match from this year and count how many opening FH kills he has. I bet FZD's percentage on opening FH kills is higher than anyone else's.
Someone mentioned XX is great against choppers, but so is FZD. Case in point, 2018 WTTTC Sweden FZD vs. Ruwen Filus. FZD pulverized most of Filus's backspin shots with is FH.