Might I suggest that you need to check more carefully what the stats you quote are measuring before jumping to conclusions about them. I've annotated the figure to highlight the rather obvious problems:
It's measuring relative productivity per hour. Before you can figure out whether that means Scotland is generating more wealth per person than the rest of the UK, you have to multiply that by the average numbers of hours worked, and the % of the population who are actually working. (I don't know how doing that would impact the results but it's bound to have some impact).
The chart also compares to the median region, not the mean GDP. That will be distorting the results because the two regions of London and the SouthEast are both hugely more productive than the other regions - and they will cause the mean to be higher than the median. Even worse, the regions are not weighted by population. The regions listed below Scotland in the chart are, on the whole much smaller than the two regions above Scotland (London and the SouthEast). Once you take those corrections, into account, it's pretty clear that the bar chart will be over-egging the actual productivity of Scotland. I don't know what the total production per head is in Scotland compared to the rest of the UK, but it is simply not possible from that chart to deduce that either the productivity or the total production per head in Scotland is higher than the UK average.
(I'm not by the way trying to knock either the chart or Scotland. The purpose of the chart appears to be to show how much more wealth per hour worked is generated in London compared to anywhere else, and it shows that very well. The chart was rather clearly not designed to show you anything about how Scotland compares to the rest of the UK, which is why you can't reasonably deduce anything meaningful about Scotland from it).
I don't know where you get that myth from, as I've never heard it before. But the fact is that Scotland does receive a considerable net subsidy in UK Government expenditure, and if Scotland loses that subsidy as a result of becoming independent, then EITHER the Scottish Government will have to oversee a massive cut in services OR there will have to be massive tax rises to make up the gap.