What I'm going to say is probably the less popular. I feel strongly against increasing Ana's damage for 2 main reasons.
Firstly, this is a blatant power/damage creep, again. When Ana was introduced and became meta with her really strong healing, Mercy was changed from 50HPS to 60HPS, just because they set this as the new benchmark as a main healer when originally 50HPS was perfectly fine and not even low. It felt like a feeble attempt to force Mercy into relevancy and understates the impact of the change. What they should have done at that time was address Ana instead of trying to creep Mercy's base heal.
Secondly, Ana's low usage has barely anything to do with her damage in the pro scene. IIRC Ana has almost always been <50% win rate on the ladder at GM level, not that it means much, and pub players will tend to favor increasing her damage as it feels more fun and gives her more control. But that doesn't mean it's a good thing or the right approach. Before the Mercy rework, Ana still saw valid usage depending on maps and team composition, with the core lack of usage being attributed to D.Va and Winston negating her heals, and dive in general. Changing her damage addresses neither of the two key reasons.
Bumping up her damage feels like it's trying to force her to compete with Mercy, creep her into Zenyatta's damage specialization, and make her feel more 'fun' to play with. I feel that there is no need to meddle with Ana's damage at this point in time, especially without first completing their iteration with Mercy. 60HPS Mercy should have never been a thing, though its impact was never really pronounced with her lack of usage in tournaments. I strongly believe that 70 damage Ana shouldn't be a thing either. There is no need for that change to ensure her viability. More likely than not we'll get to see healthy usage of Ana when Mercy is toned down, unless dive with the new D.Va is still too oppressive for Ana.
TL;DR: Fix Mercy first before touching Ana's damage. Going to 70 damage introduces more problems than it solves. If / when Mercy is finalized, then should we be looking at Ana. Otherwise, heck no, stop interfering with 2 heroes that compete for the same slot in the current state.