By 93 slayer you should have 1000-2000 slayer points total, not 400
Ipoy has mentioned above every tip and trick there is to Slayer on the server, 200m slayer exp for example is the same as 6-9m osrs xp depending on your rank, since you are looking at a x20 - x30 multiplier on average. (It can be higher/lower)

There are plenty of methods to get more points easily, using boosting methods that are described above, wilderness slayer ect. If you don't want to utilise them, like you would evem on osrs to get unlocks out the way, then that's upto you but we aren't going to be adding more points to tasks, simply because you want fast xp but no "grind" on any account mode.

You can already utilise 2 ingame features for Bonus points, Relics and Well Boosts.

You can choose to take the full task and even have options on many npcs to extend them further though the slayer unlocks.

Any task locked npcs are done to match osrs or to suffice with the reward tables (custom npcs), this again isn't going to be changed.