I believe it does drop power to regulate the temperature like other units. The wattage on the eleaf in TC mode is not adjustable from what I understand, you couldn't set it to 20W or 30W like other APV's.
I am not familiar with the Evic, the eleaf would be the same as Bikenstein setting his SX M to 40W in TC mode and vaping with only a temperature adjustment available.
It has to be able to drop the wattage or else it couldn't regulate temperature. 40 watts is the middle of the range of wattage adjustment on an evic TC, it seems to work well. I've tried higher and lower wattage adjustments on the evic TC and there is very little difference in how it vapes. Eleaf left off any adjustment to make it simpler and cheaper, performance should suffer little unless you want to vape at very high temperatures.