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).