Dimondis paints a rather bleak picture... it isn't that bad.
The game has changed radically in the past few years, but many of the changes have been focused on making the game more casual friendly.
--6-person exp parties don't really exist, because it is viable to get exp solo, with 18, or anywhere in between. The new Trust system lets you capp up to three NPCs of various jobs to flesh out a group or support you solo. Abyssea provides fast and easy exp (no, you normally don't have to pay, although lower level characters are expected to provide some particular support functions) for up to a full ally.
--It is much easier to catch up now. The new Records of Eminence (RoE) system lets you build points as your character progesses, ultimately offering baseline ilvl gear that will allow you to participate in many end-game events as you build up further. These events are fairly open; there is no 72+ hour HNM camping against the entire server in hopes of a drop.
--End game content is more forgiving and inclusive than it used to be, and much less job specific, although some jobs perform better i nsome events than others. That said, if you are returning, your best bet for entry into this is to start with a support job (whm, geo, brd, cor) and use that to build a DD.
--A number of Quality of Life improvements just simply remove many of the hassles that we used to have to deal with.
All of that said, yes, if you're interested in returning, try it out for a month or so, and ask questions.
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Renatus (Titan)
"We are Dragoons, and to make short work of foppish cavalry is our bread and butter."
-Bob Shaftoe, The System of the World