Sure Ehlers had 30 more points. But 70% he was playing against the second best forward line and the second best defensive pairing. According to your statement that he spent 70% of his time without Drouin who would have obviously had to face the other teams top players. Ritchie on the other hand had to play against the other teams top forwards and dmen game in and out.
Sure Ehlers has more skill than Ritchie at the junior level and if the Canucks were a junior team I would pick Ehlers. But the fact is the Canucks play in the NHL which demands different attributes to succeed. If Ehlers weight (162) is accurate as reported by the combine he will not be able to implement his skill at the NHL level without at least 20 pounds of muscle. Assuming his height is 5'11 and his weight is 162 he would likely be considered an ectomorph body type good luck trying to put 20 pounds of muscle on in 5 years while playing hockey.
What it boils down to is that you don't draft players on what they have done you draft them based on what they could do at the NHL level.