I think considering the 1 Tank, 1 Healer in dungeons, 2 DPS / 2 Tank / 2 Healer / 4 DPS raids shows that they're aware that DPS is just generally going to be more popular. I think it's a pretty fair spread for games, Ranged jobs are actually in a pretty similar boat to tanks/healers as they're more rare then melee, considering how much melee options we got (and we're getting more lol) It's no wonder why DPS is heavily favoured even though we got twice as much.

In DT If you combine tank and healer it's a ratio of 8 Support Jobs vs 13 Dps Jobs, So of course DPS is going to be played more theirs just more playstyles (literally aswell tanks/healers bassically have the same playstyle at this point), a lot of people want to level a Few DPS most likely even if you main tank/healer esp considering theirs three different DPS categories.

Honestly though this is a Lose/Lose situation, because if anything the current state of healers drives away more people then not, from other games I've seen tank is usually a even less popular role then healer but In ff14 it seems more common then healer, is that because tank is well designed? No It's because tank is semi tolerable but even tank has it's own issues.

Healer needs to appeal to healer players, Tank needs to appeal to Tank players at the of the day, The solution of making them "dps" doesn't fix that because DPS players want to play DPS not boring slow DPS, I'm obviously not saying healers/tank's shouldn't DPS (I actually like that they contribute a good amount of damage) but what makes doing DPS fun on tank/healer is that you're meant to be doing other things while also dpsing, with healers people can argue that you have to still heal sometimes, but throwing out a ogcd here and there isn't really cutting it for healer, what I'd find fun is having some DPS procs and extra skills but also having to actually make a choice between gcd healing or not, Tanks aggro management, stances can go, but the replacement being a even easier dps rotation? being super tanky and kitchen sinking all CDs on tank buster just isn't fun, I can only hope they give tanks more interactive abilities with the party, beyond just having different rotations to make that more fun.

This even effects DPS players, "phys ranged" on the job page says they're meant to provide support (when they don't really offer that much outside of raid buffs or one extra party mit), Beyond that they're so common that they have to switch to tank/healer a lot just so they dont have to wait 20 minutes for a single duty (I do this myself when I want to play something like BLM but it's just too much of a hassle to wait).