How is this an example of the Hegelian Dialectic?

exactly, root comment's point is that 'synthesis' is missing, so there is no forward progress unlike the dialectic!

Thesis: monoliths in one repo

Antithesis: microservices in separate repos

Synthesis: microservices in a monorepo

I kind of get what systemizer is saying. People may think of evolution of technologies as cycles but it is never that. A new technology 'Y' is always developed because the incumbent 'X' has some shortcomings. And even after a period of disillusionment when we revert back to 'X', it is not always the same. We synthesize the good points of 'Y' back to 'X'.

Coming to this topic, I see Microservices as a solution to the problem of Continuous Delivery which is necessary in some business models. I can't see those use cases reverting back to Monolith architecture. For such scenarios, the problems associated with Microservices are engineering challenges and not avoidable architecture choices.

Unless we coin the term "macroservices"...

well, we can think of the synthesis as returning to monolithic services with the understanding the sufferings of microservices.

Because the world isn’t the same after the two competing technologies have fought it out.

Sure, I don't think anyone would disagree with you on that.

But still, how is the initial comment an example of the Hegelian Dialectic?

Hegel's produces new things though