Since Henry took over ownership, I have felt like the Sox were contenders every year as we entered the season. Obviously, there were several seasons in which things didn't work out. What happens on the field can't be helped. It's the job of the GM to put together a contending team on paper. Theo, Ben, and Dombrowski have done that for over 15 consecutive years.
So yes, IMO, that kind of success can be sustained if the farm system is good enough. It has been good enough until about 2 years ago. Time will tell whether that marks the end of the run of having a contending team as we enter the season.