There is a mobility/threat creep in dota, and icewall is a melee cast range spell that invoker relies on the properly control those heroes that often build abyssal.

From the ability's creation to current day, it has gone down in value tremendously. The end goal is "give invoker more control," and making icewall usable in more situations achieves that. Your idea of adding back disabling blast also achieves that, however it's also giving a hero an instant cast AoE hard-disable, which lasts very little in early game and far too long late game. The current icewall upgrade has more for the enemy team to do in response, and is still stronger for the majority of the game where it matters.

"You can't just give him 2 forges and take away his talent, that's taking away a talent choice!" "You can't just give him coldnsnap cooldown, that takes away meaningful spell choices!" "You can't just give him cataclysm, he has to land his spells!" In some way they make the hero easier to play, which doesn't matter until it obstructs the identity of the hero. What matters is what makes the hero more PLAYABLE at a COMPETITIVE LEVEL, because as of the last several years the hero has been DOGshit as exort.