You're struggling with the word 'quality'. Your Mac mic is not a bad microphone at all, it's just characterless - and probably if you test it, quite flat in it's frequency response. The 87 has, er 'character'. If you have something that can play back full range sound from say, 50 to 20K, play some pink noise and record it on the Mac and Neumann. Then analyse the frequency response. You will see differences, and you've decided you like those differences - so you could EQ the Neumann to sound like the iMac. Quality is usually the absence of noise, the range it can hear and perhaps accuracy and sensitivity. Your Mac would probably pass most of those criteria - maybe noise could be a little higher due to the noise of a spinning drive, if it's not SSD?
Most expensive mics are bought for character - which means deviations from flat. EQ - careful, gentle and subtle EQ could move the 87 to nearer what you fancy - but so could a budget condenser?