TL;DR Hard Magic is generally 'strictly better' if you are willing to put in the effort and are capable of pulling it off, but poses unique challenges Soft Magic will simply never experience in exchange for being 'strictly worse'. The strictness ought to be emphasized, since so long as your work is written competently, only the people actually looking for the difference in quality will find it.
Hard Magic just means that the magic system is as close to 100% logically consistent as possible, with clear and defined rules that cannot be broken.
Soft Magic just means that the magic system is not required to obey any amount of logical consistency, or have clear and defined rules.
Harry Potter is definitionally soft magic. There are clearly no rules for what magic can and cannot do, with almost 0% logical consistency. It isn't even truly a single magical system as much as it is a list of incredibly specific and random stuff, as if she who will not be named was making it up based on whatever she thought of at the time with no thought to how it would exist alongside everything else.
By contrast, despite appearances, D&D magic is Hard Magic. Almost archetypally so, in fact. There is a hard and fast list of what magic can and cannot do. It's an *extensive* list, containing every spell for every slot, every class ability, every monster ability, every magic item, and so on, but it is clearly and wholly defined. It all interacts with each other in defined ways, and was intended to interact with itself. RAW is an abbreviation of Rules as written. Rules that you cannot break without fundamentally changing the feel of the setting (hence why AL and other official D&D ventures disallow homebrew and are typically less fair about RAI). Definitional hard magic, despite how chaotic and strange it looks.
Because there are two fantastic examples of Soft and Hard magic so well known by so many, I think it would be prudent to highlight that they two examples also show why the differences matter.
1. Soft magic systems are easier to write. Fullstop. No rules to follow, no reason to pay any more attention than the bare minimum necessary to complete your work.
2. Hard magic systems are generally more interesting because of their defined rules and restrictions. There's real creative value in exploring the rules of your magic system to their conclusions, logical or otherwise. Once you have a rulebook, you can compare to it, explore its implications, integrate the system as part of the setting the same way physics is.
3. Soft magic systems tend to come off as lazy, unimaginative, or boring unless you're willing to concede at least some hard defined rules. There's a reason people don't tout Fairy Tail or literally any superhero comic (I'll wait for your to think of one) as having good magic systems. They functionally don't have systems at all, just whatever the author made up at the time.
4. Hard magic systems often have the problem of writing themselves into corners. By having a rulebook, you can't bend the rulebook without fundamentally bending the audience's perception of the world your story takes place in. If, in chapter 5, the audience learns that you can't under any circumstances create matter Ex Nihilo, and then a character does exactly that in chapter 186, explanations and justifications are only going to go so far with your audience.
5. This is a weird one, but the powerscalers/gamers have a point. It doesn't really matter what the rules are or if they exist at all, the thing your audience is going to pay attention to is what your characters can and cannot do, or have and have not done. Soft magic systems are piss poor at properly showing what a character can and cannot do and what is and is not possible, making it harder for the audience to understand the implicit stakes of your magic system. If your character could pull out a anti-nuke laser if given the correct ratio of love-interest kisses + dead mentor ghost-pep-talks, it is no longer worth even considering the possibility of stakes coming from your magic system. So why have one at all?
6. The people who hate the meta character builds have a point. Having well defined rules also meanings the trappings of meta, or Most Effective Tactic Available. If you have a hard magic system, it has a meta. If no one in the setting knows what it is, it is excusable so long as it isn't obvious or readily apparent. Otherwise, You, the author need to make steps to ensure that the logical way for your setting to exist isn't everyone running around with your magic system's equivalent to Sorcadin, Palalock, Silvery Barbs spam, or DivWiz.