Maybe if I use boldface too it will make me more correct!
I, along with everyone else, mentioned that anyone choosing merits should take into consideration what jobs they intend to level and what they feel will work in their best interests. However, you should take into account that Galka PLDs tanked just fine long ago in the day and age before merits existed, before Homam existed, back when they had only their 143mp to rely on, plus some from Adaman and other gear selections. The same could be said of HP merits, true, but the point is that 143mp + gear should be enough to suffice.
Any time you are cured to full HP, your HP merits are helping you. This should happen somewhat often. However, you will rarely have full MP to take advantage of MP merits. They will more often than not amount to nothing more than some extra shaded-out area at the end of your little green MP bar, doing you absolutely no good whatsoever.
More HP is never a bad thing. Remember, if you run out of MP, you don't fall flat on your face while the nasty mob runs rampant over your allies. Running out of HP does that.
The greater the Starting Pool of Mp is the more value a Refresh Rate has.
This just simply is not true.
Starting out with more base MP only means that you have a smidgeon more MP to start with, but once it's gone it's gone
. You still
have to rely on your refresh rate to be able to do anything more. If your refresh rate is 5mp/tick with 143 base MP or 5mp/tick with 400 base MP, either way you're still getting 5mp/tick. Having higher base MP isn't going to magically make that 5mp/tick into something more than what it explicitly is.
If you're burning through MP so fast that your refresh rate isn't enough for you, then even having 400mp you are still going to run dry and be just as bad off as the other guy with 100mp.
In the end, a Galka with no MP and a meager refresh rate is just as good as a Tarutaru with no MP and a meager refresh rate. Base MP is irrelevant. All base MP does is help you last a bit longer before running out. In the case of 80mp from 8/8 MP merits, 80mp isn't going to go a long way before it is completely spent. A PLD is most likely better off using gear to get MP, maxing your Chivalry (5/5 for 10min recast), and having a nice WHM for Devotion, a RDM for Refresh, and a BRD for Ballads.
...advise should be given as to where a player is at in the game.
If a player is in the stage of the game where they are building merit points, odds are they are joining zerg groups where mobs die in 15 seconds pulling Limit Chain 100+ and the PLD is focusing on just doing as much damage as possible. Even in regular tanking role, they have already made it to 75 WITHOUT merits and should be able to manage their MP accordingly.
So, if they are meritting, MP is irrelevant because the mobs die too fast to make it worthwhile or they are in a normal role and should know how to manage their MP. If they are HNM tanking, they need HP to survive potentially deadly attacks, resulting in MP still being irrelevant. Sentinel/Guardian should be enough to generate enough hate without having to spam spells and squander your MP reserves.
As you put it, in the "here and now", a brand new Lv75 PLD (as noted by the quote: "I am not sure how the merits work quiet yet..") should be focusing on things such as unlocking Chivalry, capping Shield, capping Sword, and capping Enmity, as ScarShiva noted. HP/MP is further down the line. Putting "a couple" extra merits into MP and getting +20mp isn't going to make a huge difference in the grand scheme of things, as you seem to be implying. Those merits are better spent elsewhere.
And, in the event that it hasn't been said enough, merits are the choice of the player who chooses them. Pick what you feel suits you best and will give you the greatest benefit. Advice is based on personal opinions, which everyone has. Only your opinion matters, so long as your choices don't compromise your ability to perform the role for which your job is meant. Don't try to play PLD with -enmity merits, for example. You'll only succeed in making it more difficult for yourself.