Indeed, the additional benefits between Diamond & Plat seem quite low considering the fact that you need to spend almost double to reach the status.
I will be spending around 22 k€ in 2019 in Accor; my employees around 15 k€ and I would say several hundreds of thousands euros indirectly through my clients (that I am advising on their travel policy) and pretty sure that I'll only reach Diamond and not invitation only status.
Will see in 2020 but will probably not prefer Accor more than necessary