No one's saying WHM isnt needed endgame, WHM is invaluable in endgame. People are saying in EXP parties where you can choose the enemy you fight, RDM >>>>> WHM in most of the camps that are chosen on Nasomi. WHM does not have dispel, it cannot sustain MP, it cannot enfeeble as well in a high paced TP burn.

I play RDM late 40's right now and no matter how versatile RDM is there's no way that an EXP party can survive with a single mage without over 50% downtime. Besides, doing all magic work constantly making sure everyone is buffed and refreshed as well as debuffing and healing on top of that is too stressful for both the player and the mp pool (even with refresh). I think we can agree that an EXP party needs at least two mages and at least I believe that a WHM+RDM combo works better than 2xRDM because you need -ga and -na spells that only WHM has (though you get that in a limited capacity if one of the RDMs happens to be a /WHM). Also below level 38 you need WHM for raising.

Not needing WHM after level 41 is so untrue, and I'm saying it as RDM. RDM can never truly be a main healer because they don't have Curaga, meaning that a nasty AoE could wipe the party without the RDM having enough time to respond. They also don't get Cure V so they'll struggle at endgame. They also only get the basic Raise and at high levels that XP loss really starts to hurt. An RDM/WHM is a decent healer though, that's why I also leveled it as needed - and hated every moment of it.
I believe that a good party should have both a WHM and a RDM, with the WHM being the healer. The RDM should stick to what they're good at - Keep the WHM and themselves refreshed at all times, debuff the mobs and help cure if the shit hits the fan. I've had enough parties like that and they all work fine with hardly any downtime since the refreshes make sure the WHM never runs out of MP.

Regarding PLs, it's basically what everyone said. Yeah, for a brand new player a PL can be hindering but mind that most people in the dunes are not brand new players - some are leveling their 3rd or 4th job, some are leveling their alt (in which case the PL will usually be their own main) and some are people who played retail back at the era and already know the basics. In these cases it makes sense that they just want to get past these levels ASAP so they'll want a PL. Right now I need to level a level 21 BLM and the mere though of having to dodge goblins again at the dunes makes me want to do pretty much anything else.
I do understand why a WHM specifically would feel like that since the PL's main job is to heal, a WHM will feel useless in many cases. Party members are aware of that but they still want you because they know they'll need you later on. If WHM is your first job then you should kindly refuse any such party and explain that you're trying to learn for yourself.

...TopShelf told Nas to roll back all your ZNM gear, do the gilpocalypse and nerf Fishing/RNG into the ground.

I play RDM late 40's right now and no matter how versatile RDM is there's no way that an EXP party can survive with a single mage without over 50% downtime. Besides, doing all magic work constantly making sure everyone is buffed and refreshed as well as debuffing and healing on top of that is too stressful for both the player and the mp pool (even with refresh). I think we can agree that an EXP party needs at least two mages and at least I believe that a WHM+RDM combo works better than 2xRDM

RDM's have had thousands of EXP parties in Boyadah Tree where we solo heal with no support for a good portion of it, and we manage just fine with very minimal downtime (because our pullers didn't let us have any downtime lol). This was on Crawlers (spam Poison and Cocoon, so we need to constantly stand up to Poisona and Dispel) and Flies (Poison and Cursed Sphere, so Poisona and Barwatera).

I would certainly prefer a PL, but its not impossible without.

Fixed!

I'm pretty sure I was in one of those parties with you on my RNG Kharlan - if so, I just wanted to give you props for being a badass RDM

Fixed!

...TopShelf told Nas to roll back all your ZNM gear, do the gilpocalypse and nerf Fishing/RNG into the ground.

I had 2 EXP parties in Boyadah Tree this weekend where I was solo healing RDM with no support for a good portion of it, and we managed just fine with very minimal downtime (because our pullers didn't let me have any downtime lol). This was on Crawlers (spam Poison and Cocoon, so I needed to constantly stand up to Poisona and Dispel) and Flies (Poison and Cursed Sphere, so Poisona and occasionally Barwatera). It was definitely stressful for me lol, but we didn't have any problems.

I would certainly prefer a Support or a WHM, but its not impossible without.