And even it was, T4 Level 1 still has more stats than T3 Level 3 therefore doing more damage, and still proving to be the better option ^_^.
Although for a small period at some point plunder even for t4 atk build drops a little, so I think it's best to upgrade one by one to lvl 3 rather than switching all to t4 lvl 1 to minimize any potential damage. Also how much damage you do to an eb greatly affects your plunder bonus at the end.
When I was doing my converting from t3 to t4 I would build a t4 lv1 to replace my t3 lv3. My stats increased and there was a slight increase in plunder. It makes complete sense to first convert to t4lv1 when you get the gold and then lv2 as you get more gold. Some people do however have the personal preference to wait to go straight to lv2 or lv3 so they van see a huge stat increase
Lv 2 , T4 would be the better choice for me!! You will be converting them anyway !! Now a lv1 T4 would be less worth it, but lb 2 and 3 are !!