Even with “+%” nodes, the emblems have a more pronounced effect on 3 stars as compared to 5 stars, just because the base stats of 5 stars will always be higher than 3 stars, so the overall percentage increase in stats will always be lower for the same path.
See, Ulmer and Isarnia as examples. Both are wizards who have similar squishy stats with high attack.
If we take the attack path for both Ulmer and Isarnia, then the percentage increase in their attacks stats are 24% and 17%, respectively. That’s a huge difference. Same goes for their other stats.