Hello,
For a while, a few years go, when Agile was new, I thought that one of the weaknesses of Agile methodologies was that it was difficult to scale them. You could have a team, maybe two agile teams, but then for large projects, you ran into difficulty of coordinating between teams both business wise and technically, hence the need to have an initial stage where you had to do some architecture, design and business analysis work.
But lately, with rise of agile scale frameworks such as SAFe, you can now safely say that yes, you can scale Agile. So you can get all the benefits of using Agile (such as early customer feedback, early releases, technical adjustments) even for large projects. I have been part of projects that scaled Agile and I can safely say that it can be done (it is viable).
But beyond using various development methodologies, being Agile or going Waterfall, the most important of all is your ability to execute. You need to have the right technical people and you need to have the right key decision makers and you need to foster the right kind of collaboration environment and company culture in order to make it all happen.
There is no going around that.
Have a nice weekend,
Razvan