Here’s my napkin math. If there are holes in it, please point them out.
Season 1
Let’s assume we’re at the 30% crit soft cap from gear, which puts us at 35% crit.
Baseline, without any set bonus, 35% of heals do 200% healing, and the other 65% do 100% healing:
.35 * 200 + .65 * 100 = 135%
With the s1 set bonus, 45% of heals do 215% healing, and the other 55% do 100% healing:
.45 * 215 + .55 * 100 = 151.75%
151.75/135 = 1.124
So the s1 set bonuses give us 12.4% more healing
Season 2
2pc
The two-piece set bonus did 2% of my healing in any given run extremely consistently, so that’s easy, I do 2% more healing with that.
4pc
In the 26 waycrest I just did, the spells affected by the 4pc bonus had the following breakdown:
- healing surge 23.7%
- chain heal: 19.5%
- healing wave: 0%
with s2 4pc, surge does 10% more and chain heal does 2% more, so:
0.10 * 23.7 + 0.02 * 19.5 = 2.76
So the s2 set bonuses give us 2 + 2.76 = 4.76% more healing
And that’s for fortified Waycrest, where I do a disproportionately high amount of healing surge healing because of etch. In general, it will be an even larger difference.
Edit: for another example, +25 everbloom:
- Chain Heal: 28.3%
- Healing Surge: 9.6%
- Healing Wave: 2.4%
0.10 * (9.6 + 2.4) + 0.02 * (28.3) = 1.8
For a S2 total of 2 + 1.8 = 3.8% 
awful
CONCLUSION
S1 is 2.6-3.3x better than S2 for healing.
For damage, S1 adds > 0 damage, S2 adds 0 damage, so S1 is infinitely better.