Making it easier doesn't mean simple to the point of no optimisation.
I believe what they meant is the core of the gameplay will be more simple. Most DPS rotation will be simplified probably by having a less strict rotation or a few simplified mechanics.

For instance, the addition of the Ninja Armor Crush skill which increase the duration of Fuuton by 30sec greatly simplified the gameplay by removing the burden of perfect mudra every20 which couldn't always be achieved.
Other things such as increasing the BLM Astral buff duration by 2 secondes also helped a lot without rendering the JOB as simple as it used to be.

My guess is, they deepened the gameplay of some job rendering them more interesting and technical. However, for some of them, (like BLM for instance) the rotation is a bit too restrictive and not only does it requires a great deal of practice just to not mess it up but the sheer number of skill used to do the simple make it more complexe for no real reason.

I think with the rework of the battle systme they'll go for a less static and more reactive gameplay.

A good example would be world of warcraft DPS rotation, easy to understand, hard to master. For instance, the firemage reliance on double crit is simple, you don't need to play hours and hours to figure out the rotation as it involves only 4 main skills (+ a bunch of randoms spell/talent) and there is load of room for mistake. However, perfect use of fireblast and pheonix skill (wihtout considering overall skill in game mechanic) makes a huge difference in DPS output. Same for the mana management of the arcane spec.
Easy to understand, hard to master. Right now, some job have very punitive dps rotation and little room for mistake. (i repick the BLM), missing a split second from umbral fire cancels your FireIV, pushing one more spell and delaying the transition to UI and IceIV can make you loose Enochian. All of these have a very severe impact on your DPS. the rotation isn't easy to operate under non optimal condition (movement, mobs etc) and any mistake will be severly punished. Thus making the difference between a perfectly operated rotation and a non perfectly operated rotation(but still not failed to the point of loosing Enochian) rather small. In short, either you do it great or you totally fail it.
I believe they want to get away from that kind of gameplay.

Also, a less mechanical rotation means the player can focus more on the actual fight instead on all their cooldown procs and buff duration

I wouldn't be too concerned about it, I think they did a great job in HW by deepening the overall gameplay and experience. Some job got more loves than other (Ninja's Duality and Dream within a Dream will, imo, be revamped as they are extremly dull skills)