The overall complexity might be bigger. But I would argue that the overall complexity is not the most important factor in understading the system. The important factor is something that I would call the 'complexity of the viewing window' - that is how much complexity there is in each whole 'view' of the system. This is quite vague thought - but I'll try to explain it.

With good plugin architecture you can partage the whole code into isolated parts with low complexity, you can view each part with a low 'complexity of the viewing window'. What is more you can view the whole system with a low 'complexity of the viewing window' too - since you don't need to know all the details of how those plugins are coded - you just need to know how they are assembled.