Guild Wars 2

All are fairly solid even in the new maps. Of the ones you talked about ele needs a bit of care to survive but not a huge amount, change to a more defensive build/armour and good to go. Necro can survive anything, personally I hate minions and only began liking the proff after I stopped using them. Engie use bombs and strafe and you can survive anything on this as well. All in all if you die find out why and either change build/armour or get your timing changed to avoid the damage.

I personally like the staff ele/tempest, as he has powerful range attacks. The problem with HoT enemies is, that you have to react quick and get a feeling for when to dodge / when to just move out of the danger zone / when to run.
It depends on your equipment, too. Do you have at least exotics?

Most situations should be fine if you keep moving, keep a distance between you and the mobs, time your evades etc.
The dragon@grove is doable if you stay out of the AoE and time your jumps (when he’s doing his mega AoE). The mobs should be easily killable when you’re using staff.

Nuhoch stealth detection will take care of the mobs vanishing, it takes a bit of time to get but not much. Frogs can be ranged down I have done so but you need to be very careful to move before they let go a volley.

If you can’t beat them avoid them.

This is only a learn to play issue. Nothing wrong elementalists. If elementalists are too hard for you. Try the ranger.

if everything will be easy it’ll be not interesting to play, it’s like a challenge for you, try to make a smart strategy, find another gear or skill build

i guess Yargesh.4965 meant that you need to avoid them around by land but not their attacks

you always can ask your friends to help you with this quest

PS: sorry for my english

Regarding those frogs… you can take aftershock which gives magnetic aura. Magnetic aura reflects incoming projectiles.
Other sources of magnetic aura include
Staff Earth 3 > Magnetic Aura
Warhorn Earth 4?5? (can’t remember which) > Magnetic aura
Focus Air 4 > Projectile absorb, absorbs incoming projectiles and projectiles fired within the sphere thingy.
Focus Earth 4 > Reflect, condi remove, blast finisher
Focus Earth 5 > Immunity from damage
Dagger Earth 2 > 1/2second (maybe a bit more?) projectile block.
You can also trait for magnetic aura at the end of channeling earth overload

Ele has tons of ways to mitigate dmg, but they do indeed have the lowest health pool/armor so traits and knowing what your skills do is very important. As well as selecting traits with good synergy amongst each other.