According to
this list on Spotrac, we have missed 86 games due to injuries, which puts us only at the 20th place in games missed.
Teams like the Blazers, Raptos, Pelicans, Rockets, Pacers and Nets were hit harder.
It is a convenient excuse, but not really compelling, IMO.
Also, other teams with first year coaches have managed just fine. Just looking at this season, Taylor Jenkins looks good so far in Memphis.