Well, if to expand the definition of the word 'arranger' you have to accept keyboards that are less capable of the job, why not include dual manual organs with bass pedals. LOTS of guys can make those sound as if a whole band is playing (sort of!), and they have no content at all!
It seems to me you want to expand the definition of 'arranger' to be more vague than it already is, kind of making pointless ANY descriptive term. The whole reason to label a tool is to define it's function (or function determines the label, either is good!). If ANY keyboard with ANY kind of non-live played parts is an arranger, and ANY keyboard with ANY kind of sequencing functions is a workstation, well, most keyboards now are identical, label-wise. Which makes for some VERY confusing marketing and buying decisions.
Rather than lump more and more keyboards under the same blanket description, we need to find better and more precise labels for these hybrids. Otherwise, how does someone looking for an 'arranger' know what to look at?
Of course, 'look at them all' is a good idea, but few have the time or patience to sample the entire market. If I want an arranger, why should I waste my time driving to a Motif dealer, just because it has some quasi-arranger like features...? It ISN"T an arranger, at least if we stick to the definition an arranger has had for the last 15 years or so. And a G70 is NOT a workstation, despite even having the words on the front panel! For one thing, there is no user patch storage, a basic WS feature, or the ability to call up ANY external CC/PC# combination (just the ones that correspond with ROM voices), another basic WS feature.
Allowing manufacturers to mislabel these things, and confuse ourselves is counter-productive. Another, better, more descriptive label for what keyboards like the MotifXS are is what is really needed. 'Loop-stations', "Looparrangers', 'Arpstations', whatever... Until it has FULL arranger capabilities, it should NOT be called an 'arranger'
As to the Roland 'Prince' (the keyboard formerly known as ¥), firstly, unless the style package for it is very expensive, why would anyone buy the basic? And if it IS very expensive, why would we buy it? Secondly, style and sound-set are a VERY interlinked package (witness how poorly most styles translate to other non-native arrangers), so styles from a G70 would sound very differently on the Prince.
There ARE a few true WS/arranger hybrids. The MS is one of them. But note that you don't save much money getting one of these rather than a WS AND an arranger. Of all the mainstream arrangers, the PA1XPro is about the closest thing to what you are talking about, but it has NO loop/arp capabilities (in M3 or MotifES terms).
The thing is, hiphop and urban music have VERY different auto-accompaniment needs than more traditional styles. What works well for one does NOT work well for the other. Until the two forms of auto-accompaniment DO finally make it to the same keyboard, let us not jump the gun and start labeling them the same...
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An arranger is just a tool. What matters is what you build with it..!