But a 1st level paladin spell, for example, isn't weaker than a 1st level wizard spell. They do equivalent damage and whatnot. A 5th level Ranger spell isn't more or less powerful than a 5th level druid spell, by and large. They still use the same base damage calculations and so on. The difference is, paladins and rangers don't get 6th+ level spells, but, instead get other class effects instead.
But, since the spells are baselined based on level of spell (not the level you get that spell), they are all fairly equivalent. It's not like a 5th level ranger spell does significantly more or less damage than a 5th level wizard spell. And, they've largely gotten rid of the idea of varying spell level by class, the way it was done in other editions. It's not like a spell is a Wizard 4, Cleric 3, Paladin 5 level spell. They all appear at the same spell level if the spell appears on multiple lists.
Again, I'm sure there are exceptions, but, broadly speaking, a 5th level spell will have roughly similar effects, regardless of who is casting it.
They have similar effects, yes, but the point of access, and the usage, differ. When a caster is gaining access to 3rd level spells, a paladin is only then gaining access to 2nd level spells. When a cleric is gaining access to 5th level spells, a paladin is merely gaining access to 3rd level spells. When a cleric is hitting their cap of 9th level spells, a paladin is merely gaining access to 5th level spells. So while, yes, a 5th level spell is pretty much a 5th level spell, you have one group of classes casting 5th level spells when they reach ninth level, and another group of classes casting 5th level spells when they reach seventeenth level. That's quite a dramatic spread of when they're flinging these respective spells about, and that is an important mechanical interaction to take in to account. So, rather than making one spell X level on the cleric list, and Y level on the paladin list, they simply limit when paladins gain access to spells of X level across the board. Same basic idea, much simpler implementation.
And while the spell system itself is a cohesive whole in design, how the classes utilize them varies a fair bit. The warlock remains a prime example. It flat out sets a precedent that a caster can have a much higher usage per day. Invocations strongly push the ability to use spells that other classes have access to at-will instead of utilizing daily spell slots. Warlocks also push the ability to use their lower level spells many, many times per day, using much higher slots than most other casters.
Again, using a simple spell as an example, Animal Messenger: A wizard, capped out at level 20 with maximum spells, can summon 99 animals per day to send messages with, if they use all their slots on that spell. A warlock spending a full day casting the spell, thanks to short rest recovery and having it always cast as a 5th level spell, is summoning 240 animals per day.
A wizard gains access to two spells, one 1st level spell, one 2nd level spell, to cast as at-wills, at 18th level. By that level, a warlock has upwards of eight at-wills, ranging from 1st through 4th level spells.
In exchange for a much smaller pool of spells known, a warlock is capable of casting spells from their more limited pool considerably more times each day.
Additionally, some of the actual raw power is likewise accessible at much different rates. A warlock is adding their stat modifier to the damage rolls of their damaging cantrip at 2nd level. Only one of the schools of wizardry can do the same, and they don't gain access to that until 10th level. That's a huge difference, and means the warlock is dealing considerably more damage for a much longer period of time. What's more, that warlock is also able to add both the die and their stat modifier in damage multiple times against the same target each turn, while the wizard is merely adding the additional dice without the modifier. The warlock has much larger single target spike potential.
Because the spell lists themselves are not the only metric in play. The other abilities each class brings to the table have to be accounted for as a cohesive whole, as well.
And psychic powers are already being designed as a fundamentally different set of powers than spells. You have way less of them. But they all have some sort of passive benefit you gain while focused on them, then a suite of enhancements or sub-abilities you can use at the cost of your daily resources. You have one "active" at a time. They've also already shown that psychic powers have a slightly different range of power out of the gate.
Beacon is explicitly worse than Light in effect, the light created radiating from yourself, not from an object you touch, making it much less versatile than light in a general sense. But Beacon can be used as a bonus action, making it more versatile than light in terms of action economy.
Mind Meld, too, varies from its spell equivalent in ways that are in some ways explicitly better, and in others worse. Mind Meld is a bonus action, a consistent part of psionics in general in this edition; they are much more economical, action-wise. Mind Meld also doesn't require a somatic component, meaning it's much, much more stealthy (you have to actually raise your arm and point at the target of Message). However, Mind Meld only affects creatures you can see, while Message only requires you know where they are, even if they are hidden in a different room or whatnot. However, Mind Meld is any creature you can see in range with no other restrictions, so if you can see a creature in another room, because of a clairsentient power, or an array of mirrors, a camera and monitor, et al, then you could Mind Meld with it. It doesn't specify line of sight, you simply have to be able to see them by whatever means. There is no restriction in Mind Meld pertaining to solid objects of different widths obstructing communication, either; if you can see someone stuck in a 5 ft thick iron oubliette, no matter how it is you are seeing them, you can Mind Meld with them using the current wording of the power.
Accelerating some types of effects is similar to this. A paladin can't remove curses until they hit ninth level, but a cleric is doing it from fifth level on. An evoker can't deal extra damage equal to their stat modifier until tenth level, but a warlock is doing it at second level. And that's ok!
Pumping up the power level beyond the baseline with a limited resource also has precedent. Warlocks do this to a limited degree with their spell slots always being cast at the level of their highest accessible spells; from ninth level on, every spell a warlock casts using a warlock slot is cast at fifth level, including spells they know from another class via multiclassing. Sorcerers are the shining example of this, however. A wizard casts a fireball at fifth level, and it simply does what it does as written, the end. A sorcerer casting that exact same fireball at that exact same level might be doing so at double the range, they might be rerolling up to five of the damage dice and using the new result(s), they might be casting it as a bonus action and not a standard action, they might be casting it without verbal or somatic components, they might be giving all their allies in the effect auto-success on the save, they might be giving one of the enemies disadvantage on their save. All of these effects jump the power-level of that fireball above what anyone else can do with the same spell. And that's ok!!
So no, really, the entire complex tapestry of interacting abilities that the psionic mechanical framework ends up bringing to the table has to be considered, as a cohesive whole, to the mechanical framework of spells. It's not as simple as: a 5th level spell, is a 5th level spell, is a 5th level spell. It's much more nuanced than that, and the existing classes for spell-users show just how varied the access to, usage of, and raw power of a given ability can be, using a single mechanical framework.
