Unlike APG, I wouldn't trust Windows Defender to block all malware. Indeed, I know that it doesn't (because using third-party software frequently detects nasties that have got past Windows Defender).
However I will agree that the 'full' version of Malwarebytes has been known to slow some computers down. (That's the version that a user has either paid for gets by default for a trial period when they only want the free product anyway). That's why I generally recommend AdwCleaner, instead of Malwarebytes Anti-Malware, these days. It's 'out of the same stable', so it works with the same database of malware, but it doesn't require installing; you simply run the downloaded program. (As it's not 'running in the background', or periodically updating itself, it can't slow a computer down. Yo just download and run the latest version whenever you want to carry out a malware scan):
https://www.malwarebytes.com/adwcleaner/
Historically though, one of the most common causes of computers being slow to load/run has been Microsoft's own anti-virus software 'getting stuck in a loop'. It was a program component called MsMpEng.exe that was behind the problem, as it pulled vast amounts of a machine's resources when it continually tried to update the anti-virus program. That problem persisted across Windows 95, 98, Me, XP and 7. (All written from experience! It was probably there with Windows 8 too but I've never used a Windows 8 machine). It's possible that something similar might be going on with your Windows 10 machine, so it could be worth giving third-party software a go instead, to see if it makes any difference. Try Avast:
https://www.avast.com/en-gb/index#pc
Also check which apps run automatically on your laptop at Start-up. Type 'startup' into the Windows search box and click on 'Startup Apps'. Disable anything you don't need.
If all else fails, reset your PC (which reinstalls Windows), taking great care to select the option which retains all your files:
https://support.microsoft.com/en-us/windows/recovery-options-in-windows-10-31ce2444-7de3-818c-d626-e3b5a3024da5#bkmk_section2