The verdict

CPU
Dell OptiPlex 7070 Micro has 1.5x the CPU throughput (8,038 vs 5,307 PassMark).
Plex
GMKtec NucBox G2 transcodes more 4K HDR streams (~5 vs ~3).
Idle power
GMKtec NucBox G2 idles lower (6W vs 12W) - cheaper to run 24/7.
Networking
GMKtec NucBox G2 has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
Dell OptiPlex 7070 Micro takes more RAM (64GB vs 12GB).

Which wins for each job

Job Dell OptiPlex 7070 Micro GMKtec NucBox G2
Plex / Jellyfin ~3 streams ~5 streams win
Frigate NVR ~4 cameras ~4 cameras
Proxmox / VMs 8,038 PassMark win 5,307 PassMark
Firewall / router 1 NICs 2 NICs win
Local AI / LLM no slot no slot

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec Dell OptiPlex 7070 Micro GMKtec NucBox G2
Price (list) $160 $159
CPU Intel Core i5-9500T Intel Processor N100
Cores / threads 6 4
PassMark 8,038 5,307
iGPU UHD 630 Intel UHD (24 EU)
NICs 1 2
NIC model Intel I219-V 1GbE (chip unlisted)
RAM max (GB) 64 12
M.2 free 1 1
PCIe slot none none
Idle (W) 12 6
TDP (W) 35 6