what is skill locking good for? i know that quest reward xp is distributed to all skills so it makes sence to lock skills to level a few skills faster BUT skills level too by using them, so if i use more skills i should gain more xp overall and in the end i level faster, right?

i just started the game and atm it feels like i get most xp in battles, i mean i cast heal 2 times and get 2 "healskill" level ups, same for fireball, even though i started as lightning mage and since my spells hv high cooldowns and my weapon attack doesnt do any dmg i might aswell throw a fireball and a heal from time to time, right?

or does it change later and it is better to just level a few skills?