When developing a site on the CMS, are modules written or is the CMS running around?

Question

CMS

In theory, as I understand it, modules are written for all additions, but in fact, I see that this is all done right in the template, as well as in open cards, if we say so without modules in WordPress or opencart, what does it threaten? after all, it’s really faster, I’m making plugins like a fool ...
And what if we need changes in the admin panel, we will affect the core and update then we won’t be able to, it’s as bad as it is in this case?

Answer 1

If you need to do it tomorrow, the site will work for one week, and then it will be deleted - then it is done as quickly as possible.
But if you need the site to work for a couple of years, then only modules. Otherwise, you won't be able to update.

Answer 2

If the client already has everything that is possible, then the logic is written in the template, the files of the CMS core are edited, some kind of combine is stuck for the sake of 2-3 chips, etc. The main thing here is speed, the client needs something to work in the morning. It is too expensive and cumbersome to change or maintain such software, so if you need to finish something or fix something, this version is thrown out.
A more correct approach is to create modules and / or components that add some specific feature to the site. Basic rule: one chip = 1 plugin. Look at Wikipedia about GRASP and SOLID, I always start from them about designing something more or less serious and long-lived. This approach is used if the client's site will live for a long time or if the site will have a large number of installations on different machines under different environments, with not always all modules installed (I mean PHP modules, for example, libxml), etc.
From my own experience, I can say that usually there is always something in between, and, depending on the qualifications of the developer, it is more shifted towards item 1 or item 2 at the same time.