There is quite a bit of variability in how NHL teams (and AHL teams) use the ECHL. At one end of the spectrum you have Toronto, who has signed multiple AHL contracts the last few years and stocked their ECHL affiliate. It hasn't always resulted in a winning team at the ECHL level. The one advantage is that those players can't be called up to other AHL teams, so there should be less roster turnover - although if the Maple Leafs and Marlies have a lot of injuries, the Growlers could end up shorthanded. This also means that the NHL/AHL team is probably signing those players with their own priorities in mind, and maybe not with any particular care to building a good ECHL team. They may sign a lot of talented players, but not enough PKers or leaders in the locker room for example. Also, if the team isn't doing well, or certain players are underperforming or have attitude issues, the ECHL coach has less latitude to make changes.
At the other end of the spectrum would be a team that doesn't assign any players to the ECHL, and simply uses their affiliate to take ECHL contracted players to fill in roster holes in the AHL during the season. This gives the ECHL coach/GM more latitude in choosing their own roster, so they might end up with a better mix of players. However, those players can also be called up to any AHL team, so depending on how well they play, and how close the team is to other AHL teams, they could get picked apart. Also, they will have a hard time signing more high end talent, since they don't have the AHL team paying the majority of those players salaries. The connections the ECHL coach/GM has in this model are key in having a successful team. Other factors can play into it also. Florida has an easier time recruiting players vs Reading for example, just because of the climate. Reading has the advantage of being within an easy drive of Hershey, Allentown, WBS, Binghamton, Syracuse, and Utica, so players more interested in callups than beaches might prefer to be here.
St John's won't have either of those advantages, so aligning with a team like Toronto might have been their best move. Portland may have trouble recruiting too, although they are close enough to the New England AHL teams that they may get players called up there. Riley Armstrong is a first time head coach, so he doesn't have too much of a reputation or name recognition to draw players. New teams (whether expansion or moving a franchise) tend to have a harder time recruiting the first year. The Royals were similar to Portland in that they were a relocated franchise, but didn't bring any player rights or staff from Columbus. The first year they just weren't skilled enough to compete. They played hard, and were entertaining, but didn't have enough top end skill to compete.
Also, teams have different philosophies about releasing contract information. For example, there was an article in our local paper yesterday where the coach mentioned that he has a few more players signed, but they haven't released their names yet. The Royals like to spread the announcements out over the course of the summer. Some teams announce the signings as they occur. Some teams save all their signings and release them in September, just before training camp opens. So judging a team based on what they have announced so far can be misleading.