Hmm, if I translate that into phrasing that makes more sense to me, I think what you're saying is that levitation is not so much problem for low-level creatures (who anyway have low hp and are easily killed), but rather for smallish, high-hp creatures who lack flight or any ranged options. It makes them much easier to defeat than otherwise, particularly in solo fights.
I'm saying that one of the modern theories of D&D design is that combat shouldn't come down to a single saving throw or dice roll. That is to say, most people agree now that, "Save or Die" isn't particularly fun. Applied against monsters it makes fights trivial rather than exciting, and applied against PC's it leads to frustration because if the whole fight turns on what you threw on a single die, then your choices matter relatively less.
Let's look at either scenario. Suppose you have a "Black Knight" or "Beserker" or "Orc Chieftain" that you intend to be a particular sort of challenge. That foe has no effective missile attack and no ability to fly. For a party without Levitate, the challenge represented by that foe might be adequately described as say "Challenge Rating 9". But if the party has Levitate, then they have a "win button" that they can use to win the fight outright in whatever percentage of cases the foe fails a single saving throw. If the saving throw is failed, they dangle helplessly in the air some number of feet off the ground, and the party can dispatch them with leisurely missile attacks with either no risk or negligible risk for a supposed CR 9 challenge.
Similarly, a PC with similar characteristics can find themselves dangling ineffectually for all or most of the fight just because they failed a single saving throw.
Now, that isn't necessarily bad per se but it is a problem that 5e on the whole seemed to be trying to get away from. Aside from the problems of balancing spellcasters with noncasters what it creates is design constraints that DM's have to be aware of if they want to create interesting challenges. We already had this sort of problem to an extent, in that if the whole party can fly then any monster that lacks flight or effective melee attacks can be trivially defeated, and as such above a certain CR all monsters have to have ability to deal with that or else they are badly designed. (The Tarrasque is a classic case in point, and please note the 4e attempts to deal with the limitations of the design.) What this does is lower the point to which that becomes a major constraint.
In general, prior editions usually also had save or suck spells with various narrow limitations. But aside from the problem this creates in balancing an encounter that meets the scenario the spell is effective in (is it CR 9, or should the very existence of the spell lower the CR of such creatures), what you tend to discover is that if you allow too many of these things into the game (as 3e did, especially as the game was expanded in supplements) you end up with spellcasters with a tool for every occasion always able to attack the weak point in whatever monster they face.
But in any event, the ability to use levitate as an offensive spell - and a potent one at that - vastly increases the power of the spell compared to prior editions and consequently, one wonders why it remained a 2nd level spell. For example, the ability to dual purpose the spell as both effective offense (removing a monster from the combat) or defense (removing yourself from melee) reminds me most closely of 3e's 'Resilient Sphere', but this is in some ways more abusable than 'Resilient Sphere' in that you can with 5e Levitate still attack the creature you've removed from combat. Resiliant Sphere was a 4th level spell. The question people are focusing on is the irrelevant question of which is better, 5th level Telekinesis or 2nd level Levitate. The important point is that this is a vastly better spell than it was in prior editions with unchanged level in an edition of the game that much more greatly limits access to high level spells.