I doubt you would string 4 top rated graphics cards together and add a second CPU to run a db. The HW spanks Apple Pro for a fraction of the price... You need to get your Mac models straight. As far as I know, Apple has only announced that a redesigned Mac Pro would be coming. They didn't give a timetable or any pricing info. It may not even make it out this year.
You're trying to compare your Dell beast to the iMac Pro released last month. You know, the all-in-one Mac model with the screen built in? It was designed for a somewhat different market and is also, I think, mainly a stopgap machine to appease the Mac professionals who weren't happy with the 2013 Mac Pro. Think graphic designers and film editors who can justify that expense. Many of them will move on to the more powerful Mac Pro whenever it gets released.
Sure, the iMac Pro isn't cheap, but even the base model makes a kick-ass desktop machine, and you have the advantage of being able to run macOS natively on it. Or Windows and Linux too, if you so choose. Can't run macOS natively (or legally) on a PC with making a hackintosh, and I bet you couldn't do it at all on that Dell thing.
Yes, the 2013 Mac Pro design was clearly a mistake. I thought so at the time, said as much on another investing site (and probably here too). Apple finally admitted it admitted it themselves in April of last year.
I'm guessing the new Mac Pro will be more like the previous tower model, affectionately and derisively referred to as the "cheese grater" because of the look. It was a great modular design. You could add multiple graphics cards, hard drives, and optical drives internally, and it had external expansion ports similar to PCs of the time. The new Mac Pro probably won't be as big, due to Apple's obsession with smaller form factors these days, but I'm holding out hope they get it right this time.