No-one is disputing that Virgin are improving. The issue is that Virgin are over promising and under delivering in terms of J product. On 2 of my DJ flights last week, there were 5 equipment changes over a few days, so the concept of not selling business on 700s doesn't work, as they cannot consistently deliver a specific aircraft on a specific route at a specific time.
Another different layout just exacerbates the risk of disappointing their J customers. Maybe the issue is too much change too quickly. From a customer experience perspective,it may be wiser to use the new aircraft in place of XFA and XFB, allowing the immediate refurb of these two planes rather than having months or years of inconsistency whilst they expand routes with the new planes.
With the Embraers, it appears as if they launched J without a plan at all. I've yet to encounter a refitted Embraer - they seem to be getting a curtain and seat cover makeover, which suggests quite some time until the full refit occurs (though personally I don't mind the spare seat, it is costing DJ revenue, with 2 fewer J seats).