Three years ago.
The Pro12 still provided 3 of the 8 quarter-finalists and 2 of the 4 semi-finalists in the Champions Cup. Yes there are some shit teams in the Pro12, but there are also poor teams in the Aviva Prem and Top14.
By the way, actually half of the teams in the Pro12 come from the bottom two ranked 6N countries - Wales and Italy.
Scotland are currently ranked 5th in the world, above France and Wales.