Not wishing to burst anyones bubble, but the announcement of 3 times a week to SNN is hardly the precursor to a base in LBA. On the same principle a similar launch from MAN last year would have indicated they could expect more!
As for would a base in LBA hurt MAN, probably not so much now there are already options available from other airports anyway, MAN focus has to be more on the longhaul than shorthaul anyway.