As a Joomla (novice) developer, I'm concerned about why we really need modules to create our own forms. I'm definitely not an authority on the subject when it comes to Joomla but here's my issue.
I understand (through hands-on discovery) that we can create forms using two ways (without additional custom modules).
By writing the form content straight in the index.php page, then checking for submit using PHP.
By inserting the HTML content for the form as a CustomHTML article using the admin back-end. Then have a separate PHP page to do the processing and return back to a specific landing page.
First I'm not sure if the above methods are considered sane in the joomla world but I do think they're workable.
If so, why do we need to run through rough seas trying to download and install form-builder plug-ins and write code that looks pretty absurd with so many files.
The first solution you mentioned is the worst that could be done. Editing the index.php should never be done. If an update for the template is bought out and you install it, it will override your changes.
The second point you mentioned is also a bad idea. There is no point in using separate PHP pages if you're using the Joomla CMS.
Stick to Joomla standards and create a custom module (not custom HTML module) either by coding it yourself or getting started with a Module Generator.
The whole point of using a CMS is to make life easier. A Joomla site is built of of Components, Modules and Plugins.
Components are like applications such as a Forum, e-commerce system etc. Modules are like widgets such as a twitter feed, shoutbox etc.
Plugins change the behavior of something.
why do we need to run through rough seas trying to download and install form-builder plug-in?
Trying to download and install a form builder is not difficult at all. Simple go to the Joomla Extensions Directory, go the the necessary category, click on an extension that suits your needs, download and install it and voilà.