Can someone please explain this . . .

[Adler]

I'm PS4 player and I don't have space for mark numbers in hotbar nor have I fingers fast enough to set them in the middle of a fight so I just tank without marking and switch targets constantly trying to keep aggro on all targets at the same time. I think as the one blm mentioned before - players able to deal massive damage usually are capable to notice what tank can and can't do and adapt.
I have had dungeons where whole run both dps will always attack fifferent targets but those usually are brain dead people that can't do enough damage for me to lose aggro. Smart and skilled, the truly powerful dps just quickly notice that tank can't keep aggro and adapt to tank playstile very fast.

[Gardes]

I'm PS4 player and I don't have space for mark numbers in hotbar nor have I fingers fast enough to set them in the middle of a fight so I just tank without marking and switch targets constantly trying to keep aggro on all targets at the same time.

You can just use a mark macro and even attach it to lob if you want to. I use a controller and I have enough space on my cross bar for separate lob and mark buttons.

/mk Attack1 <t>
/ac "Target Forward"
/mk Attack2 <t>
/target <attack1>

This is what I use. I only use up to 2 marks because anything past 3 mobs, I would want my party to start using aoe. 3rd mark is unneeded because that'll be the last mob to be alive so that's obvious enough. This macro would mark my current target, quickly select the next target and mark it as 2 and then quickly return to my first target as I run it to lob. If the 2nd target needs to be a specific one, I can just mark it as number 1 with the same macro as the first target dies.