Im currently using a elelock in end game and have a good experience of the class usage.
later in earth tower/end game you will definitely have more spells to use to fill your rotations, but you’ll need to use them in a way to be able to do so. however that being said, there will be a couple seconds of downtime once ALL your spells are cast. in this scenario you can either use the time to re position or to autoatk, however in end game parties, you will have a chronomancer with you at times. this will enable you to have NO downtime at all because of pass. this meaning you will be permanently casting something basically, and the mobs will die faster than you can cast.
To answer your OP, yes sleep is heavily used in end game and at i would reccomend to max it or to get 14 points of it. you can leave ebolt at 1 point if you want the filler+knockback but im actually using lvl 14 energy bolt, this is because after testing, i personally like the filler damage of it and i can also do a substantial amount of damage of it in tbl/pvp against squishies. of course, this is also because other spells in the wizard3 branch arent really worth taking. lvl 5 surespell/quickcast/magicmissles should be auto included, but you can spread your extra points into either lethargy or ebolt, dont touch equake or reflectshield, you’ll need at least 1 point in lethargy for the strike attribute debuff though.
some ending notes: dont worry too much about the build at rank 4-5ish, you have long cd’s for a reason, you will get more spells in the future, as well as your mastery of using certain spell combos or paths will improve.
Also some notes about reflect shield : it scales off SPR, but as a elelock, you will be using either FULL INT or a variation of INT + CON. thus reflect shield is actually garbage. the reason why you feel reflect shield is okay at the moment is because you are low rank/low lvl atm. once you get to higher levels and against stronger mobs, reflect shield is horrendous and takes a buff slot. (there is currently a buff limit in the game)
so if you have too many buffs, you’ll over write the previous, perhaps more useful ones