Cantrips are supposed to be relevant at all tiers of play.
Spells Known and Prepared (p. 164). A new paragraph appears at the end of this subsection: “If a cantrip of yours increases in power at higher levels, the increase is based on your character level, not your level in a particular class” (6th printing).
For extra confirmation, that's official errata to the PHB, listed in the errata thread in this very forum.
It only seems broken when compared to non-optimal choices. Full casters can (and likely should) be casting full leveled spells most of the time to play optimally - with the exception of the warlock. Full martial characters get boosts to their damage around each tier also, via extra attacks or increased sneak attack damage or other. For most characters except the warlock, cantrip casting will become less significant as they level - a low priority choice in their options for actions. Warlocks have boosts to their cantrips to keep them even more relevant.
For example, your rogue/lock is missing out on spell slot progression, invocations, and spell choices (as well as class features and an ASI) from being rogue 3. You still only have 1st level slots and only 3 known spells (instead of 6 known and 3rd level slots at lock 5). On the other side, you are also missing out on another sneak attack die, uncanny dodge, and an ASI from rogue for those two lock levels you took. Low level multi-classing is often where the trade-offs are most painful (and where therefore cantrip scaling looks most appealing).
Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item. Members of a few classes, including bards and sorcerers, have a limited list of spells they know that are always fixed in mind. The same thing is true of many magic-using monsters. Other spellcasters, such as clerics and wizards, undergo a process of preparing spells. This process varies for different classes, as detailed in their descriptions.
In every case, the number of spells a caster can have fixed in mind at any given time depends on the character's level.
the most recent addition seems to ignore that, and leave it up to the DM's discretion
Need to know
Cantrip scaling is based on Character Level, not Class Level.
Your Rogue 3/Warlock 2 launches two beams when they cast Eldritch Blast.
My DM's Guild Content - Mostly quick rules and guides.
really? seams kind of broken?
Cantrips are supposed to be relevant at all tiers of play.
Spells Known and Prepared (p. 164). A new paragraph appears at the end of this subsection: “If a cantrip of yours increases in power at higher levels, the increase is based on your character level, not your level in a particular class” (6th printing).
For extra confirmation, that's official errata to the PHB, listed in the errata thread in this very forum.
My DM's Guild Content - Mostly quick rules and guides.
It only seems broken when compared to non-optimal choices. Full casters can (and likely should) be casting full leveled spells most of the time to play optimally - with the exception of the warlock. Full martial characters get boosts to their damage around each tier also, via extra attacks or increased sneak attack damage or other. For most characters except the warlock, cantrip casting will become less significant as they level - a low priority choice in their options for actions. Warlocks have boosts to their cantrips to keep them even more relevant.
For example, your rogue/lock is missing out on spell slot progression, invocations, and spell choices (as well as class features and an ASI) from being rogue 3. You still only have 1st level slots and only 3 known spells (instead of 6 known and 3rd level slots at lock 5). On the other side, you are also missing out on another sneak attack die, uncanny dodge, and an ASI from rogue for those two lock levels you took. Low level multi-classing is often where the trade-offs are most painful (and where therefore cantrip scaling looks most appealing).
Yes, which is why taking two levels of Warlock is very popular with a lot of min/maxers
Please know that you will not be able to add sneak attack damage to an eldritch blast as it is not a finesse weapon or ranged weapon.
Known and Prepared Spells
Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item. Members of a few classes, including bards and sorcerers, have a limited list of spells they know that are always fixed in mind. The same thing is true of many magic-using monsters. Other spellcasters, such as clerics and wizards, undergo a process of preparing spells. This process varies for different classes, as detailed in their descriptions.
In every case, the number of spells a caster can have fixed in mind at any given time depends on the character's level.
the most recent addition seems to ignore that, and leave it up to the DM's discretion
it was purely an RP thing
not trying to optimise
just was really unclear on how eldritch blast worked