You are asking why the UK would be weaker without Scotland. I do not understand why you do not find convincing the very claims you already concede? 10% weaker is weaker, specifically by 10%.
I do not find it convincing because reduced GDP does not equate to weakness. It has to be viewed in context: GDP would be reduced but per capita GDP would not be reduced by 10 percent (because the population would also be lower). Furthermore, the UK spends more on Scotland than Scotland contributes, so it's a net economic burden. Independence would remove that burden, leaving the UK better off.
I think I have already expressed this perfectly clearly in previous comments, so this is the last I will say about it.
Is West Germany better off with East Germany or without? Or how about is California better off with Alabama or without?
By all means continue to shrink yourself down into the smallest tribal sub-population you can slice yourself into. I’m sure prosperity is right around the corner when you finally do.
I think I have already expressed this perfectly clearly in previous comments, so this is the last I will say about it.