The WOL and Mass Murder

[Cilia]

Contradictions:

No, the Echo has manifested itself more that just boosting our combat ability.

The Warrior of Light is not known to use the Echo to boost their combat abilities, or even be able to. (The "Echo" buff given when failing old content is most likely just a gameplay mechanic given a slight lore gloss - why doesn't the Warrior of Light use it right away, for example?)

Also both Lahabrea and Igeyorhm implied we could tear open dimensions.

In the context of the fight against the Ascian Prime, it's implied that the Echo literally grants the power to violate Hydaelyn's laws ("What walls are these?! Damn you, Hydaelyn!"), at least as far as the separation of souls goes. This idea actually does fit most if not all of the applications we've seen the Echo used for (beyond the aforementioned gameplay applicaton).

The reason we see most telegraphs is due to the Echo.

If you want to lore explain attack telegraphs with the Echo, you need to have something that works with everything. Autonomous warmachina still have the same telegraphs despite being machines, and whether primals have genuine souls is highly debatable, but they produce the same telegraphs as everything else.

If you do the summoner questline, it's mentioned that we could control stronger egis and even primals, but it's too risky because we might lose control.

As I recall the reason that was given for being unable to summon more / new egi was because egis are constructed in part out of the Summoner's own aether, of which the Warrior of Light has a limited amount (Echo or no Echo). This was why Ramuh-egi couldn't be summoned (the Warrior of Light was already using all their aether for Ifrit, Titan, and Garuda), necessitating the research into Trances to gain greater power during the Heavensward SMN arc. (How this was overcome during the Stormblood arc I can't recall, if it was explained at all).

[Iscah]

As I recall the reason that was given for being unable to summon more / new egi was because egis are constructed in part out of the Summoner's own aether, of which the Warrior of Light has a limited amount (Echo or no Echo). This was why Ramuh-egi couldn't be summoned (the Warrior of Light was already using all their aether for Ifrit, Titan, and Garuda), necessitating the research into Trances to gain greater power during the Heavensward SMN arc. (How this was overcome during the Stormblood arc I can't recall, if it was explained at all).

They never went back to the question of summoning the other egis. We have Bahamut now; what more could we want?

Maybe they're hoping to just not bring it up again so they don't need to create the new egi types. (Then again, we still need to have something new to learn in future expansions, right...?)

At a more in-game level, I did see an interesting theory (though can't remember where) about why we fail to summon Ramuh-egi at the Singing Shards - over in the Monk job quests, Widargelt talks about how the monks train in places "where aether flows strong" to bond with the power there, but it can only attune to one person. The Singing Shards is where we fight Tristan at the end of the ARR summoner questline, and he summons an egi there - so it's possible that he absorbed whatever power was there, and so there is none left (or at least accessible) when we try to summon Ramuh-egi in the same place.

[ObsidianFire]

At a more in-game level, I did see an interesting theory (though can't remember where) about why we fail to summon Ramuh-egi at the Singing Shards - over in the Monk job quests, Widargelt talks about how the monks train in places "where aether flows strong" to bond with the power there, but it can only attune to one person. The Singing Shards is where we fight Tristan at the end of the ARR summoner questline, and he summons an egi there - so it's possible that he absorbed whatever power was there, and so there is none left (or at least accessible) when we try to summon Ramuh-egi in the same place.

Initially summoning Egi doesn't work by absorbing energy from the surrounding area though. Instead it's using the elemental aspect of a location as a reference point to make your own aether attuned to that elemental aspect which matches the elemental aspect of the Egi you are trying to summon.