I like my HDs replaceable
Aside from various Windows machines, I run a 2007 iMac and a 2010 MacBook. The iMac is now on its third hard drive (HD failures in 2010 and 2015, each replaced with a larger disk), and the MacBook on its second (HD failure in 2018, replaced with a larger disk). For all three HD replacements, I was able to switch the disks myself (which would not be the case with a soldered-in HD). Also, Time Machine was my friend on all three occasions.
For me, reliability is much more important than weight or thinness.
Both machines are now up for replacement as they have outlived the upgradeability of their operating systems. I hope their replacements run as well and as long.