I wouldn't pay too much attention to it for a few reasons
1- Beside the WHM, most job won' receive any adjustement but numbers, and it is unrealistic to expect every job to be well balanced on release.
WHM is a bit special since a lot of people complained. However, as many other people pointed, we don't know how healing will be in 4.0.We don't know how much heal will be required in 4.0
One thing every expansion in WoW thought me, do not base too much assumption based on what you're currently playing.
For instance, in WoW 1.0, healers had huge mana issue and overhealing was a serious business, healers were suppose to use various rank of the same spells (different potency) to match what healing was needed in order to save mana, they were also stop casting in case someone else healed before them.
WoW 2.0 gave healer nearly unlimited mana, but damage were very unpredictable and quick, this made smart heal (your heal targets based on missing hp) extremely important. Some fight couldn't be cleared without enough smart heal as damage came too quick and too randmonly to be done manually, especially in the last raid, sunwell.
WoW 3.0 had their spells rank consolidated to a form you currently know in FF14, (fast heal, heal, big heal for instance), damage became less spiky and more in line with what you currently have in FF14 except that fight required healers to spam a lot, they had no time to dps, not that their dps mattered in any form or shape. Also, many situationnal heal were introduced, basically, "timed heal" you place it while no need is required and activate when needed. The goal was to make healing more interactive and everyone's business.
From this moment, the subsequent expansion only brought new or refined mechanics, but the core idea on "how you should heal" was fixed.
You can consider that FF14 is going through another maturing phase.
2.0 jobs were extremely basic from a gameplay perspective, if you take a look at what healers in WoW can do for example, you'll get to realise that FF healers had actually very little variety. How can I put it, they were very very main stream. (Like WoW in 1.0), basically they had safe design. WHM for instance: Fast heal, heal, Big heal, aoe heal, big aoeheal(HoT), Regen.... yeah... you covered it. These are pretty "basic skill, they have nothing unique"
3.0 properly started giving jobs more identity and more interesting and fun spells to use, Assize, Essential Dignity, Deployment tactic etc. However, if you take a good look, AST and WHM felt very similar in gameplay, but AST had the cards, and WHM had nothing special. SCH was in a good position with interesting mechanic and choice.
Now, in 4.0, they basically try to refine these things and clean a bit the mass that has accumulated over the 2.0 and 3.0 by removing useless spells, consolidating them etc.
For instance, when WHM screams that they're loosing what's making them unique, Divine Seal, you see how poorly developped the WHM job was.
What makes you a special snowflake is your ability to do30% more heal every 90sec? That's rather sad.
In WoW for instance, in 2.0 if you asked someone "What comes to your mind when I tell you Holy Priest", great spells like Prayer of Mending, Cirche of Healing, Binding Heal were all great tools totally unique to Holy Priest. They were great and fun to use.
This is why the WHM is the only healer receiving a proper new mechanic, from a mechanic persective, AST and SCH receive nothing new, AST will be played the same with 1-2 new tools so will SCH with a few adjustement regarding the fairy.
There's the lily but also that new shield mechanic.
Now, people are concerned that THIS won't be enough (and I agree with them, it feels very underwhelming for a job that should become "ZE HEAL" ).
But every game and every expansion people had this kind of fears, because they compared to what they know, but things can drastically change from one xpac to anotheri
f we just take a look at WoW (and don't believe WoW is very different from FF14... they're actually very similar game in many regards, Yoshida was an avid WoW player before stepping into this project, and he actually forced the dev team to play the game when tehy were developping 2.0, you don't recreat the wheel everytime) we can see how huge the change from 1.0 to 2.0 to 3.0 were. And FF14 change are as deep in many regards.
Not only the jobs but the way raids are handled.
We don't know how raid will be and after a few tweaks, the situation might be very bright fr the WHM, we all know how astro were in 3.0
So,, I would say, dont pay too much attention to it and if you wanna play WHM, go for it. (unless you aim for top server first)