Your math is a little off. The renew glyph also increases total healing by 5% (length of HOT, and hence amount healed, reduced by 3/15, or 20%. Each remaining tick increased by 25%, so 5% increased healing overall). Wow, 5% I hear you say, and yes that may only increase your total heal by 20-30 hp. But don't forget your HPS of renew increases by 25%. That is why it is a good glyph.
Then there is the dispel glyph. Sure free heals for FC, and when carrying a nice total health, very worthwhile. But for the dispels on those with more "normal" health pools, it isn't so impressive.
And damage isn't percent based. So would you take a dispel heal of 45-50, or 25% hps? What if your target doesn't have any dispellable debuffs, your renew hps is gimped by 20%. What if you're on offensive dispelling? Then your glyph is worth squat.
So not so black and white,
unless you're a niche FC dispel spammer. Then yes, you are correct, it is the best