Unlike older games, where you get healing touch 1, 2, 3, 4 as you level, if you want to heal more, you upcast the lower level spell. Still, in this game healing spells are fairly worthless outside of healing word, since potions are better. The main purpose of healing word is to stop characters from dying when they are knocked out, so they can then use a potion and get back in the fight.
The game gives a decent amount of +spell attack, but even without it, Gale should have been over 70% hit chance, when on higher ground, for most of the game on his real cantrips, as long as you boosted his Int to max as soon as you could (level 4 take it to 18 or 19, then level 8 take it to 20).
There was an issue with the firebolt that Shadowheart can cast, being tied to Int, instead of Wis, so it always had shit hit chance. Also, the cantrips granted by items worked the same, I think. Where they had shit hit chance because the were going off a stat that the character may not have had bonuses on. Clerics are supposed to melee anyway, so they have harder time hitting with cantrips to begin with.