It means that TAP doesnt think EU261 applies - so your only choice is to pursue this further via the courts or a 3rd party that takes a cut of the winnings

You can credit your Iberia segment to any oneworld program retroactively

You are also eligible to claim original routing mileage with AC - if the mileage you earned is less than you would have originally.
But there is no basis for a refund of any kind if you flew in business on LHR-YYZ.

AC has an official close the gate 15mins before departure policy - so unless you made it at 15:01, it doesnt matter that the plane was still there and/or people were still in the jetway