You have compared the 5600 XT to two other cards in the RX 5000 series, then say ( in the title no less) that is is comparable to a card that has no specs listed in this article and is from a different GPU series ? It also seems that it should also be compared to the RX 5700 not the RX 5700 XT . Just being picky.
Judging by the UK pricing, with the 8 GB 5500 XT starting at ~£180 compared to ~£270 for a Vega 56 and ~£300 for the 5700, I too would expect the 5600 XT to have somewhat similar performance to the Vega 56, as the 5700 is similar to the Vega 64. The pricing on these is going to be interesting given the above £120 window between the 8GB 5500 XT and the RX 5700 - I wonder how it will compare to the GTX 1660 / Super / Ti cards in price/performance terms?
Performance is likely to be relatively predictable, slotting in between a 5500 XT and a 5700. It's probably going to be a little faster than the 1660 Ti, but might not be much more than 10% faster than a 1660 SUPER, which will almost certainly be priced lower.
Pricing is everything, and based on the underwhelming 5500 XT pricing, I'm fully expecting another yawnfest out of the 5600 XT. A 6GB version of the card might be "okay" at $250, provided they don't cripple it with an 8-lane PCIe connection or something, but I wouldn't be surprised if we saw higher pricing than that.
And really, it's hard to get excited about this card after the competition has reigned uncontested in this price range for the last year. Maybe if they had released these cards back in the summer near the launch of the 5700 and 5700 XT, but at this point the 1660 Ti has already been out for nearly a year, and even the 1660 SUPER has been out for a couple months. Plus, with consoles featuring raytracing hardware arriving in 2020, and support for it on the PC side of things gradually increasing as well, it brings into question how well any of these cards will hold up in the long term. A year from now, there might be mid-range cards with semi-decent raytracing support, with big titles universally supporting it, and all these cards might be relegated to running games at medium settings at 1080p.