It is very easy to recognize that Limbaugh is no journalist.
Wrong. Limbaugh reviews and discusses politics from his own perspective. That makes him a commentator, not a journalist. Every journalist who ever lived (and even fictional ones) is/was a better journalist than Limbaugh could ever dream to be.
Let's look at it objectively.
Contra "journalist": He's chiefly and above all things an entertainer, a pundit, and a commentator; this much is undeniable. If we consider "journalist" and "entertainer/pundit" to be mutually exclusive professions, he clearly falls more into the latter category. His show is nearly 100% editorial. He does minimal investigative work personally. Finally, to the best of my knowledge, he doesn't regard himself as a journalist.
Pro "journalist": He has a research staff and (believe it or not) a fact-checking staff for at least some journalistic research. He's been the instigator of numerous "call out" stories (which I loosely define as a high-profile individual drawing attention to a comment or tweet that otherwise largely escaped public notice). [Like it or not, "call out" stories are a central part of journalism circa 2019. The pages of major newspapers are full of them.] He does on-air Q&A interviews with ideologues and legislators, which is
sine qua non journalism. Finally, the format of his show is undeniably similar to that of many other pundits who
do consider themselves journalists.
As I said earlier, I regard "entertainer/pundit/commentator vs. journalist" to be a spectrum in the 21st Century. When we consider the sum of the above facts, it seems to me we can reasonably place Mr. Limbaugh at (5-15% journalist, 85-95% entertainer/pundit/commentator) on the spectrum. I personally wouldn't regard anything short of 50% as a "journalist", but I can also think of big names in US news not far from this same point on the spectrum who
are widely regarded as journalists (@Mashmont provides a few names).
Something else to consider: political cartoonists, whose work consists entirely of satirical cartoons and short editorials, are considered journalists and are even subject to receiving major journalistic awards such as Pulitzer Prizes.