I think it's called choices - and we don't have one. We get all the CPU, and none of the GPU. I would go for Iris Plus in a heartbeat (eGPU is definitely not viable, I get that), offer it as an upgrade option. Just because YOU are happy doesn't mean that everyone is.
But you do have a choice...you can go buy or assemble yourself a PC pretty much however you want, depending on how much cash you have on hand. To paraphrase Queen, "If you want it all and you want it now" Apple is going to frustrate you to no end.
While an Iris Plus GT3e iGPU is definitely better than the UHD630, it would have pleased very few and would have limited the mini's CPU to a 28w U-Series, which would have added at least another $100-$150 to the cost of the Mac mini because those CPUs cost quite a bit more than the i3-8100B ($117), i5-8500B ($192.00) and i7-8700B ($303.00).
A Core i5-8259U has no price listed, the Core i5-8269U is $320.00, a Core i7-8559U is $431.00. Apple is not going to eat a ~$130.00 price difference for a 4-core max laptop CPU when they can put in cheaper, more capable desktop CPUs that can sustain higher performance over a longer period of time at a lower cost use to give us an Iris GT3e GPU. If they did, I would be highly ticked off. It just makes no sense. Imagine the $799 model costing $949 or $999 w/ 8GB/128GB SSD...that would have ticked off
everyone even more and Apple would not have been able to offer 6-cores as a BTO option
Offering even one of the 28w U-Series as an upgrade option also makes no sense as who exactly is going to pay more for a "weak sauce" 28w 4c/8t Core i5-8269U w/Iris Plus when than they can have a 65w 6c/6t Core i5 w/UHD630 Graphics.
Please tell me why an eGPU is not viable? Because you are only getting x4 PCIe lanes of bandwidth instead of the full x16 that runs off the CPU? Well, you are not getting that from a 6-core Core i7-8750H, 8850H or Core i9 8950HK in those expensive 15" MacBook Pros either. The same would go for the mini, you would be getting x8 PCIe lanes for the dGPU, which would have most likely been the Radeon Pro 555X, maybe the 560X. Ugh...waste of money and engineering time.
If Apple had gone with the Kaby Lake-G, the Vega GPU gets x8 lanes, although it is on die with HBM memory and despite it having an 8 in its naming, it's still a Kaby Lake CPU with only 4-cores/8-threads. Apple would still be able to offer four Thunderbolt 3 ports, using the remaining x8 lanes available off of the Kaby Lake-G, but then that would indicate that the SSD would need to run through the Intel PCH. I suspect Apple found it unsatisfying to them performance wise. Or maybe it prevented them from using the T2 chip.
I readily admit that not everyone is going to be happy with what Apple chose, but it is what it is. Learn to love it, or leave it, unfortunately.
