Take a look at the airtop 3 https://fit-iot.com/web/products/airtop3/
It's not a laptop and not specifically made for travel but a very solid PC all passively cooled, no spinning parts and with great specs. Might be a bit hihger in price compared to Alienware but might be an option. I like the option of two SFP+ ports for 10G fibre (I do a lot of NDI stuff).

vMix makes good use of the GPU, not that much of the CPU (well depends on what your settings really are). So my main focus would be on the GPU, than CPU. I use Xeons in all my streaming machines and I'm very very happy. In combination with a high PCI lane count a superb GPU and NVMe PCIe storage these systems allowed me to do everything so far.

A note on Laptops. A streaming laptop is not light weight, nor silent, nor independent from power (+2h) and they have big heat problems by design. The really "only" advantage they have is that you have a "KVM" included. Said in an exaggerated way.

I have a feeling that the problem lies with the G Series, there a bottleneck somewhere.

I think it has to do with the i7 VS i9 CPU possibly or heat management.

I bet the whole problem is because of nvidia Optimus. As you can read here a Laptop with switchable gpu (UEFI Setting) with NO nvidia optimus is needed to get the best performance.

I run vMix on a Alienware 15R3 with a i7-6700HQ and a GTX1060 (no Optimus) with 4 Cameras, NDI Sources, 2 x stream encoder and 1 recording at once without any problems on a 1080p50 project (exept the poor color gammut of the panel).

Today I get me an HP OMEN17-cb1272ng. That's a fair cheap device with a 100% sRGB-Panel. The manufactor told me that there's no Optimus going on there.
So I'll try and report :-)