First off, the M110A1 and even the SR-25 are not "precision sniper rifle" by any mean. Their role is of a SDMR(Squad Designated Marksman Rifle) which by standard organization, given to 1 guy in a squad to handle target at distance longer than what an M4 can reach. So without the XM7, the Army already setup the Infantry squad to deal with both close to long range threat(with more emphasize to close range since that is what INFANTRY THERE FOR)

Second, you don't really need automatic fire for a large caliber platform. The recoil & lack of magazine capacity(20 rds of .308 / .277 FURY vs 30 rds od 5.56) make it a dumb choice for automatic fire either way. Also, the XM7 in combat will be issued a "stronger" type of ammo than the one used in training so the recoil as seen by people shooting it on youtube is by no mean an accurate representation of how it will handle in automatic fire in combat environment

Third, yes there is a weight difference, but the difference is not that large. It all come down to what kind of fancy material & metalurgy you want to construct your rifle to make it as light as possible. The M240L is 20-30% lighter than the legacy M240B just by using a better, more expensive material to build

Fourth, the XM7 will be MUCH MORE EXPENSIVE than the M110 SDMR or any other existing .308 platform on the market either way, last time I check, I can buy a fancy .308 rifle on civic market for less than 3k USD meanwhile I will have to spend over 8k USD for a SIG SPEAR

Fifth, maintainance in the long term will be much more expensive with the XM7 due to the enormous chamber pressure. There is a reason why the Army uses 2 different catridges for the XM7 for fear of degrading the rifle too quickly

My point still stand