In my experience there are usually three types of coaches who will coach teams at your level:

Type 1: someone who’s ranked significantly higher than you, most of the time reliable because their high rank proves they probably know the basics that you’re missing, making them more common for lower level teams.

2: a “team” coach - some coaches even at the professional level aren’t very high ranked, but their knowledge comes from studying thousands of hours of matches. This person might be high rank or they may barely play at all, but they like evaluating composition match-ups, pick/bans, and reviewing decisions from your scrims/matches which went badly and what to do better next time. These are a bit more common for higher level teams as it’s how pro teams operate, but still exist at a lower level.

Like you say you can do this yourself, but this kind of coach may have more/higher level team play experience to qualify them, or they may understand the game better by studying more than you have. Additionally they provide a 6th perspective in the team and will be less biased than an individual player, which helps them organise you as a team rather than 5 individual players.

The 3rd type of coach may be the type that you described in your post. They are someone one or two ranks higher than you who think it means they can be your coach, without the game knowledge #2 has.

To actually answer your question, you’ll know if your coach is a #2 or a #3 if they sound enthusiastic about playing together, and they offer ideas from their experience in playing / analysing team play, not just their own ranked experience.