The first point I would see as significant, the second I would see as meh.

Believing that the threats faced by the US/Europe/Israel /regimes in the region is increased by a merger of Al Qaeda and some other group (and thus, by implication reduced by having a smaller Al Qaeda while said other group goes its own way) seems an obvious form of believing something without the slightest bit of thought being put into it.
Yes, a larger Al Q presumably then has a few more human resources and a few more material resources, but was that what was limiting them in the first place?
Yes, a larger Al Q could, conceivably, now have more intelligence sources and thus a non-linear effect could kick in, but is there any evidence that sympathetic groups are not already sharing intelligence?

Meanwhile, since we’re all supposed to think like economists these days, whatever happened to the idea that competition is better? How about the possibility that a separate Al Q and other, in competition for hearts and minds, is spurned to be more aggressive and more innovative? Sure, one could talk about Coassian co-ordination difficulties, but such difficulties only occur when co-ordination exists. Al Q and other are not buying and selling from each other, or much interacting in any other way (apart from, as I said, probably ocassionally sharing intelligence) so that argument for size strikes me as a non-starter.

The above argument may strike you as flip, but in what sense is it actually wrong? People like Rodney Stark are treated as serious scholars for claiming that the strength of religion in the US is due to the competitive market in religions in the US as opposed to most other countries.