The gospel is too precious and powerful to simply be assumed. This is why measuring gospel articulation is so important, and an important indicator of church health.
I believe it’s very important to clarify what the purpose of the groups are, and ensure they are meeting this purpose, and include this with other measurements about group numbers and attendance.
Numbers matter to God, because people matter to God. You only need to look at the parable of the lost sheep to see that individuals matter to God (and particularly those who are lost).
I’ve been asking a lot of ministers how they measure their ministry progress, and while nearly all agree that measuring is a good idea, most are still thinking through how to do it.