When I enter content in posts/pages’ WYSIWYG editor, I do not get <p>
when ending paragraphs, just  
s. If I manually place <p></p>
in the HTML mode, they are stripped as soon as I switch to ‘visual’ mode.
This is repeated in several sites (I thought it was the theme but it isn’t).
I have read dozens of topics and answers, but none solve my problem.
I tried add/remove wpautop
in my functions.php file but nothing helps.
I do not want to use a tinymce plugin.
I have done extended research and found the answer – I am now using a hook on ‘tiny_mce_before_init’.
Based on other answers (special thanks to answer #2 @Chip Bennett), I have used the following code in my functions.php to secure the paragraph breaks (in the editor HTML mode they show as   but become paragraphs on the front-end):
You can find on the tinyMCE site the different possible configurations.
you could also say that TinyMCE is integrated with WordPress and the HTML editor strips out some characters in favour
 
… this was originally for security and the belief that we didnt need<br>
or<p>
anymoreYou can try the CKEditor
WordPress CKEditor