Devotion gives us additional skills, useful (or sometimes useless for a particular build) stats, but it could give even more. Let’s take Viper as an example, it reduces Elemental resists by 20%, that’s fairly unique, but what if other devotions instead of giving some random stuff like increased HP regen (not really random though) by 15%, gave -4% reduced resist to e.g. chaos or converted 5% physical damage to aether? That would be nice for some builds (although I think the conversion would be a bit pointless).
Some constellations are really boring, since you mostly add the same stats in completely different trees, like cunning is available in nearly every tree that deals physical damage and some trees (fox for example) give cunning twice (15 in first, +20 in third star). I am sometimes like, “I need useful stats for that character! I need to pick that skill from this constellation!” and I very rarely look on the little ones that provide large amount of chaos/order etc points, because they don’t really offer enough good stats to pick them. I sometimes end up picking Quill because I need Green and Violet points, even though I don’t focus on elemental damage or casting skills - it just gives +3/+3 so why not just pick it because of 6 for 4? Converting a particular damage type to another would sometimes force players to pick something else, because that particular constellation doesn’t give a useful stat, but, in fact, makes our character weaker (let’s say we focus on aether damage, we play Death Knight, we want to pick quill only for the points, but the first star in Quill gives “10% aether damage converted to elemental” and “5% physical damage converted to elemental”, why would we pick that?). Because of such solution, we’d much rather pick random (or more like other) trees only because they gave better stats than before, right now it’s just like “I’mma pick this one because I need some points for my Whirlpool”.
My other example would be Toad. I try to pick it for almost every melee character if I can afford it, because it gives fair amount of lifesteal. The vitality resistance is good to have, I’d pick that, spirit and OA, sure, spirit will give me some additional mana and mana regen, worth it, OA - crits are welcome, I’ll even boost it later on via my equipment, from 10 I have now 14. Now we have lifesteal, finally, I really need that. Aether and Vitality damage, well I don’t need that, but it will give me useful points, green and violet, it is worth it - additional 10 damage would be okay, I guess… There are some (very few) trees I’d go no matter what because they feel worth picking, even if they’re tier 1. Dryad would be another one, free heal in the skill, also, useful stats - I’d pick it along with turtle if I needed some points. Spider is another one, 3% spirit and cunning, bonus damage to insects, attack speed and movement speed reduction via retaliating, good for casters. 6 points for 5? Well, worth it.
Basically, it would be very worth to make other (smaller) trees worth picking due to them granting useful stats. Sometimes we don’t want to cover the entire screen with effects.