I own four bikes that range from ~17lbs to 24lbs. Except when I'm climbing the most ridiculously pitchy ascents, I cannot tell what any of those bikes weigh while riding them.
When I get home and have to lift them up to hang on the wall, sure, then I always prefer the lightest bike!
But for 99% of the riding I do, once I throw a leg over and start pedaling I can't feel those small weight differences, especially if I've got two full water bottles in the cages.