Hybrids are great for recreational and fitness riding, but you are right, most hybrids are not competitive in either world. If you are an aggressive mountain biker, you might want to consider just getting a road bike for riding with your son and keep your MTB a true MTB. If you aren't worried about competing or pushing the limits on pavement or off, then a hybrid is a good choice. It is possible to hybridize your MTB with some pavement friendly tires and maybe some sprocket ratio changes and still keep it quite capable off road with just a tire change.
I ride a Giant Boulder SE, that I put Bontrager H4 Eco tires on. The rear cassette is a Shimano 11-28 and the front end is an Alivio crankset with a 48 tooth #3 chainring. I stiffen up the adjustable fork for road riding and soften it up when riding unpaved back roads, fire trails, etc. The drivetrain still has plenty of range for both on road and off road (I don't do aggressive hill climbs but I suspect this would be a weak point even with more aggressive tires). I have ridden in non-competitive on-road group rides with this bike and it performs admirably. I'm assuming that a higher end hybrid would be perform even better.
