Steve, for most churches any growth at all would be something to crow about. The fact that JWs have managed even modest growth, in rapidly secularising societies, such as the UK is quite remarkable.
A few Pentecostal groups have grown in the UK, but these are churches that consist almost entirely of immigrants, largely from Africa and the Caribbean. Their numbers have been boosted, not by making converts in the UK, but by new arrivals from more religious countries. This does not count as endogenous growth.
Plus it is telling that the older Pentecostal groups, which do no tend to attract new immigrants, such as Assemblies of God and Elim have declined as well.
As for SDAs, my personal (and pretty extensive) experience of the church in Scotland is that they are 90% immigrants, mostly from Africa and the Caribbean, and some from Asia and Eastern Europe, with fewer than 10% born in the UK. They number around 1000 in Scotland and they are not increasing at the moment.
From what I remember the SDA church in Australia and New Zealand also largely consists of new arrivals from the Pacific islands, Africa and elsewhere. They are not converting numbers of outsiders to the church.
Incidentally JW growth in the UK in recent years relied to some extent the arrival of immigrants - from Poland in particular. The difference is that immigrants only form a minority of JWs in the UK.
JWs have simply performed better at holding back the tide of secularisation than other Christian groups. Whether that’s “something to crow about” we can debate. On the one hand they are not doing as well as they used to, or as well as some might expect of God’s endtime messengers. But they are clearly doing better than most other Christian groups in the same hostile secular environment.