After looking through the maths behind it myself, I honestly think this is the most bizarre change imaginable. To put it into context, E. Reprise currently grants -20 Mana, takes 2.2 seconds to cast, and deals 220 potency, so 100 potency/second. Jolt grants +6 mana, takes 2.5 seconds* to cast, and deals 250 potency, so 100 potency/second at bare minimum SpS. The second you stray above 2.5s GCD, so for instance at 2.48s GCD like Alphascape gear, Jolt is 100.8 potency/second and mana positive, allowing you to get more melee combos, even with overcapping. And on top of that, you're 26 mana better for using Jolt over E. Reprise

I don't want to get too into the maths however to prevent our mana from overcapping before going into Manafication with the new 110s CD (or 120s rotation for raid buffs), it's actually better to use a Single Target moulinet providing you're at close to, if not over 70|70 as it's more potency/second (133.33) than E. Reprise.

On top of this, as Yue has said, it's sometimes better to not cast at all for extended periods of movement because those E. Reprises you used could've cost you a full use of the 2270 potency melee combo.