I just wanted to go a bit more into detail.
This is correct, but for the wrong reasons. First and foremost, moulinet gcds are all 1.5, whereas melee combo gcds are 1.5, 1.5, 2.2, 2.5, and 2.5. Second, 5 moulinet costs 200 mana, but a single melee combo costs only 125, since two of the skills refund 21 and 14 mana respectively.
To find the most correct way to do it, you have to calculate the pps gained from doing the alternative action over your normal spell rotation, multiply that pps gain by the duration, and divide that number by the mana spent, and you arrive at "extra potency gained per point of mana spent".
For your baseline, in this case, it's what you do against 2 targets. Jolt II is 250 potency, higher than verthunder/veraero's potency of 240 against 2 targets, so you use that. And, of course, you use impact at 220*2 = 440 potency. 250 + 440 / 5 = 138 potency per second.
An encanted moulinet does 400 potency over 1.5 seconds for a PPS of 266.6666(repeating). Subtract your 138 potency per second of the baseline, get 128.6666(repeating) PPS gained. Multiply that by the 1.5 seconds duration and you arrive at 193 potency gained. Divide that by 40 mana spent and you get 4.825 potency gained per mana spent.
A melee combo puts out 2270 potency in 10.2 seconds, for a PPS of ~222.549. Subtract your 138 pps and you arrive at ~84.549. Multiply by the duration again and you get 862.4 potency gained, and divide by the 125 potency spent and you arrive at a hefty 6.8992. Almost 43% better of a use for your mana. So yeah it's better to use melee combo over moulinet at 2 targets.
For those curious, at 3 targets, the gains come out to 7.35 potency per mana for moulinet, and a stark 1.5136 potency per mana gained for the melee combo. It's an interesting contrast. At 2 targets, melee combo is far stronger. at 3 targets, moulinet is far stronger.