Don’t argue with the consultants.

It is not a hill worth dying on.

And you don’t know the big picture, but the little picture is everyone agreed the consultants were the right way to decide before you were there; arguing implies the people who sign contracts and write the checks are wrong; and business decisions are about the whole business and engineering exists to support the business - not to optimize itself.

To put it simply, the decision has been made by people with more experience in your organization’s culture, more authority, and a better understanding of the business as a whole.

Plus your here on HN because you have not convinced the stakeholders.

Good luck.

That really depends on they type of consultancy, the terms of the engagement, and where the responsibility lies (for both the requirements and the outcomes).

If the consultancy was brought in to do the move from Heroku but not build or run anything beyond that, then I would normally expect the client to set the tradeoff between DevEx (argues for EKS) vs simplicity/operability (argues for ECS). In that case, it would be perfectly reasonable for the OP to input into that decision.

It's definitely worth speaking to whoever is responsible for engaging the consultancy - there should be an agreed Statement of Work and at least a rough RACI matrix for each deliverable, showing who the stakeholders are and how they interact.