This, among other considerations, biased me toward the 124 over the ND. We got a better looking ND, with the more reliable NC transmission and a solid punchy easily upgradeable engine.The MT6 problems you have seen for the MX5 are ND related (2016-present)? The 124 uses de NC MT6 which is more robust.
Reading about the ND manual transmission on Miata.net, it sounds like a catastrophe. Huge issues in the 2016-17 model years. Later improvements but reason to suspect there are fundamental design flaws that could seriously impact longevity. I might have been content with the 180HP 2L engine but almost certainly not with the 155HP version in a slightly used one, but probably not so I would want to turbo it eventually...however not with that transmission.