mATX is an objectively superior standard if size is no issue. Just because there are currently a lot of budget mATX boards compared to ITX doesn't change that, it just means you have more options. For instance a $170 MSI B650M Mortar runs circles around a $260+ MSI B650I Edge at being a PC motherboard: superior I/O, much better expandability and no annoying chipset fan for nearly $100 less.
In the case of the C4-SFX v2, 13.4 vs 15.4L barely even matters considering most of that volume difference is in height, meaning the desk footprint is almost identical, which is what people actually care about.
ITX is just an objectively limiting form factor:
- need more m.2 slots? though luck
- want to add a 10GbE network card? too bad
- need a PCIe capture card? never happening
- want an easy RAM upgrade? need to replace your current DIMMs entirely
Some try to frame this debate as "ITX vs mATX", when it's actually "mATX / ITX vs ITX-only".
You gain a lot of flexiblity by allowing mATX, and literally all it costs is 2cm less vertical space above your case. You can still use any of the great ITX boards if you prefer.
When you get close to 14L and above, ITX-only stops making sense very quickly.
