Fonts in scrartcl.

The headings are far from being messed up. They are just tagged differently. And the KOMA Script manual tells you quite clearly how you can get what you want.

\documentclass[english]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{blindtext}

\setkomafont{disposition}{\normalfont\bfseries}

\begin{document}
  \Blinddocument
\end{document}

Since KOMA-Script 3.20 the classes provide an option egregdoesnotlikesansseriftitles that deactivates all sans serif defaults of the KOMA-Script classes. So with

\documentclass[egregdoesnotlikesansseriftitles]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{blindtext}

\begin{document}
  \title{Title}
  \author{Author}
  \maketitle
  \Blinddocument
  \begin{description}
    \item[An item]\blindtext
  \end{description}
\end{document}

you will see the same fonts for title and heading as with article.

The option was a result of a comment of @egreg to Why does KOMA-Script mix serifs and sans-serifs?.

There is also an option emulatestandardclasses to make scrartcl even more article look-alike.