Air Transat squeezes the seat width to 16.5" while AC is closer to 18". It makes a difference.
Only on the TS A330-200 is it narrower and on the TS A330-300 seat width is identical to AC at 18".
Also I wouldn't call Club Transat pseudo business class as it's more economy plus or premium economy. It's a decent value for the upgraded service and inclusions like dedicated check in counters and extra luggage not to mention the extra legroom but it's not even up to the same big roomy old style biz class seats most sked airlines have since updated with the pod style.