Is it possible to create plugin making and editing HTML tables? I.e. to merge cells, columns, rows, insert rows/columns etc? I mean specifically WYSIWYG editor for HTML based tables, because Markdown tables are a trash, sorry for admitting this fact, in spite of existence of other plugins to work with MD tables. Also, it’s currently possible to insert HTML tables as code in Obsidian, but in case if they are long then such tables are displayed only after scrolling down of their HTML code, which is not convenient.
It should be possible.
You’re not the only one who dislikes Markdown tables (which, to be clear, are a common third-party expansion, not part of actual Markdown). The documentation for iA Writer, after explaining the basics, says, “Let’s be real. This is a mess.” 
You might be able to view tables more easily by switching to Reading view (which annoys you less is a matter of taste).