Assuming I don't drop this computer and smash it to bits, I'll be able to keep it as long as my last MBP (a 2015 I bought new). So conservatively, let's say 5 years.

At $30/month, Mighty would be $30 * 12 * 5 = $1800 over that time period.

I paid ~$2500 for this computer, and use it for:

1) Browsing 2) Coding 3) Video and photo editing 4) Graphic design

So all things considered, while yes it's literally cheaper in terms of direct dollar and cents comparison, in terms of functional ROI, given that this computer runs a browser instance with zero lag or latency at all, it's a no brainer to just invest in the good laptop vs going with Mighty.