Are E-Hero's viable at all?

If you are asking about a E-hero themed deck, not right now.

You can mirror wall + skyscraper right now but....

Only up to 5 extra deck monsters.
The selling point of the E-Hero deck is fusion summoning monsters that you need for specific situation and since you can only have five, It limits this deck's ability greatly.

Example: thunder giant, flame wingman, terra firma, tempest, Steam healer, phoenix enforcer, Mariner

E-Hero Stratos which allows you to search for a Hero you need is not out yet.

in short, to many missing cards and too small extra deck size for a proper E-hero deck.

A Neos deck can be used with the 8th Full Box: Galactic Origin.
Example: Instant Neo Space equipped to
Elemental HERO Storm Neos

If you want to know useful E-heroes outside of E-heroes themed deck,

Woodsman 2,000 def and can search polymerization 1/ owner's standby phase.
(Galactic Origin Box)

Blazeman 1,800 def can search poly when normal/special summoned and can also send to graveyard e-hero monsters from your deck (if any).

Lady heat can deal 200 effect damage x number of e-heroes you control during your end phase.

Clayman 2,000 def (normal Monster)

Wildheart - 1,500 atk /1,600 def but unaffected by trap effects.

Heat - 1,600 atk but gains 200 more atk per e-hero you control including himself


Special Mentions
Neos 2,500 atk / 2000 def
but you might want blue eyes white dragon instead.

others are not yet available in game such as bladeedge and ice edge.

Not at the moment. They are not viable enough to compete against the best decks out there.

Hero are super slow right now their fusions revolve around a level 7 monster in a meta where Econ and Wall of D. Basically no their deck sucks in a 20 card came

Yeah but certain support is probably too powerful for Duel Links so you'll probably see mostly weaker support.

One of my decks is a hero deck.
It was good enough to win games in king of games with it but i wouldnt rate it much higher than average.

It currently looks like this:

Monsters:
Hero Blazeman x3.
Sergeant electro x3.
Hero heat x3.
Hero neos x3.

Spells:
Oversoul x1.
Tribute to doomed x1 (to get neos in the grave if i pick it up before blazeman can send him to the grave).
Enemy controller x2.

Traps:
Birthright x2.
Mirror wall x2.
Wall of d x2.

You dont need the exact cards but roughly these monsters and such support spells.

I dont have Righteous justice yet. You could tryfind a spot for it.

Skill:
-Where the heroes dwell.
-The tie that binds.
-Beatdown.
-Restart.

A 3rd mirror wall instead of 1 wall of d could be useful if you use the "where the heroes dwell skill".
But i dont have mirror wall x3 and i dont aim to get one for heros when they are average.

But to answer more of your questions.

Elemental heros seem average at best right now.
The next box will introduce more neospacians + support and also the fieldspell neospace.
Which makes it so that you dont have to use the endfase effect of neospacians.

This next box will widen your options but I dont see it turn elemental heros into a meta deck or something.

It is with new support,to date they are decent.If konami stop giving us neo spacian crap(see the new box for details)yes.Btw the new box has gladiator beast so neo spacian are even worse in that pack.

if you're asking this you're probably new to the game.