I followed a blog by an ex-Microsoft developer who worked at the company for 20 years. He only ran Defender on his machines saying it was as good if not better that most of the anti-virus software. It gets critized mainly for its lack of features and interface but not for his ability to detect viruses.
I go back to the era of Prodigy and Compuserve in the late 70's and have run software from Microsoft since MS-DOS. Before Defender I used antivirus software but I didn't rely on it, I employed the principles and practices of being safe online; never install software from dodgy sites, backup files, create periodic system images, don't modify UAC settings, don't use an admin account, and on and on. This to me is your best protection.
In all my 45 years online I have never had an incursion except for the occasional PUP. Something tells me that in addition to giving Defender a whirl, you ought to be asking yourself how did I get 544 trojans.
Good luck with your test of Defender.