I prefer Str acc on my tanks whether I'm playing of healing. My dps cut off changes by less than 5% if at all while healing and dpsing a tank in Str vs Vit acc. You should be switching to healing before the 1000 hp ever becomes relevant.

Also tank (str) and healer dps aren't mutually exclusive and both can occur at the same time. Saying that vit acc allows for more healing dps and in turn greater total team dps isnt a valid argument because objectively the most dps will be achieved with healer dps and Str tanks both doing increased dps. Taking away one or the other results in an opportunity cost and less dps potential.