The split memory of the ps3 has some disadvantages but also many advantages. If anything the ps3 has the most o f the three with regards 1080p games and also 3D support. I think the ps3 had something like 25.6 GB/s for video and 19.2 GB/s for main memory.  Where as wii u is only 12.8 GB/s for main memory. 

Most open world games suffer on wii u. Watch dogs for example.

Xenoblade is always a spanner in the works trying to access the capabilities of a console because the original looked fantastic on the wii which only had 11 gflops for its gpu. It's purposely designed to impress but the engine itself has very weak texturing and a very basic physics engine. The wii u game enables you to walk through cars because the game engine couldn't afford the collision detection routines. It reminds me of Factor 5 on the N64 they achieved miracles by hand coding time critical parts and made efforts beyond normal developers to optimise their games. Rogue Squadron on the gamecube still looks amazing.

Many ps3 and 360 games use texture streaming from hard drives to maintain a detailed attractive world at all times in open world games and this just isn't possible on wii u.

Again Watch dogs was very difficult development on wii u due to lack of hard drive, the game often has missing graphic features or textures, much slower frame rate especially under high load but at least doesn't suffer from lack of vertical sync which both the ps3 and lesser extent the 360 suffer from. The xenoblade system of installing to wii u memory or external hard drive is obviously a similar system but a far fewer number of wii u owners could do that.

The wii u would have been a perfect competitor for 360 and PS3 back in 2006 as its overall capabilities are broadly similar to those platforms. Some games would be weaker and some stronger but in 2012 for a console to have inferior  ports to consoles which are just being dropped by their manufacturer seems ridiculous. 

Still love my wii u and enjoy playing many games on it but Nintendo's rubbish tech, high price, massive profit approach is really getting on my nerves nowadays.

PS3/360 wouldn't be able to run XCX though, they simply don't have the RAM for it. Open worlds filled with stuff are memory intensive, and Wii U had double the memory of PS3/360. Hell, in the case of PS3, since it's memory was partitioned into 256MB chunks for video and system RAM, Wii U could devote considerably more than twice as much memory to, say, video data.

Regarding bandwidth, PS3's 25-19GB/s was all it had for all operations, whereas with Wii U, its eDRAM offered sky-high bandwidth for operations that needed it, meaning its main RAM simply didn't need to be as fast, because the eDRAM was there to take a lot of the load off it.

And games like Watch Dogs aren't really good example for the Wii U's full capability as they weren't exactly high priority ports with a ton of money and effort poured into them. It's kind of like judging PS3's power by its many poor quality ports.

All this being said, I do understand your frustration that a system released in 2012 didn't overpower 2005/2006 consoles in all ways and by a large margin.

Remember with the ps3 you have two types of memory so it effectively has 44GB/s overall. Where as I think wii u is something like 60GB/s for its edram (could be wrong) but that is only for 32MB. Anything the wii u needs outside the 32MB edram has a very low bandwidth of 12.8GB/s and remember that 12.8GB/s memory is a bank of 2GB of which 1GB is reserved for the operating system. So its less than 12.8GB/s + eDRAM.because the operating system is also accessing it. Same with ps3 but only one cell processor is used for operaitng system I think.

I honestly don't know how either ps3 or 360 would handle xenoblade but I suspect it would be a lot better than you realise properly programmed. Somethings would be better and others worse. Xenoblade seems designed to offer impressive visuals on weak hardware by keeping textures low resolution and by omitting many normal graphic features. The original wii version and later 3DS version both work well on weak hardware.

No they couldnt' have. Treyarch didnt have anywhere near the influence or pull that IW had at the time. For all intents and purposes Treyarch was the B team. THey were more at the mercy of Acti than IW was. Whatever Acti told them to do they did it.

Wii U's main RAM + eDRAM bandwidth is a lot higher than PS3's main RAM + video RAM bandwidth.

And 32MB of eDRAM is quite big for a system like Wii U; it's the same size as Xbox One's ESRAM, and more than three times the size of 360's eDRAM. The whole idea of eDRAM is that it doesn't need to be that big because you only use it for tasks that require high bandwidth, like your framebuffer and some CPU/GPU ops.

Open world games on PS3/360 are full of compromises also, most notably nearly always poor framerates, something XCX notably does not suffer from.

I just don't buy that if Treyarch had gone to Activision and said "the hardware is just too weak to the run the game", that Activision would have said "find a way". They showed no qualms about skipping Wii before.

I dont think it was ever an issue of it not being possible, but an issue of IW just NOT wanting to work with the Wii as they didnt want to compromise their vision. I dont buy that Treyarch went to Activision and wanted to work on Wii or Wii U out of the goodness of the8r hearts(especially since it wasnt the whole team working on it). Activision probably said ok IW you dont have to do it, we'll get some of these guys to make it instead

Oh I'm not saying it was all Treyarch's idea, I simply think that if they'd wanted to weasel out of it, they could have.