You see, so far the whole character build of the villain has been internal. In other words, creating the bad guy by thinking about the bad guy. But there is no doubting that the antagonist is defined by their relationship with the protagonist - a least in terms of how it serves the plot. The dynamic between these two forces basically defines your story. And the surest way to kill any potential tension and excitement? By making the skill, intelligence and power between the forces of good and evil completely unequal to the point of disbelief.
There are two ways in which this can play out: when the antagonist is clearly far more powerful, smart and all around greater than the good guy, or when the antagonist is a gibbering mess that has absolutely nothing on the good guy.
Let's start with the first type. Please don't mistake this with classic underdog stories: in all of those stories, sure the good guy may be out of his depth in a technical sense, but the gap between good and bad is not insurmountably huge. What the protagonist lacks in sheer skill she makes up in spirit and effort. And if it's a sports movie, plenty of training montages.
But that's the thing: after going through trials and tribulations, the protagonist finally gets into a position where they have a fighting chance. Any victory to come will feel well-earned.
But it's when that gap becomes too big that it ceases to be an underdog overcoming the odds and more about sheer luck and catching the all-powerful antagonist out on a fluke. The bigger that gap, the more you as the author will need to stretch to find that chink in the armor that brings down the nigh-invincible villain. And because the protagonist is then put into a position where they have to work to exploit a weakness, such victory feels poorly earned because it is not down to the protagonist's force of will and gumption, but rather using a kind of cheat to bring down the bad guy. In fact, it can even put the protagonist in a bad light, as this whole business of stooping to find a weak point and rip the bad guy apart with it is something many feel should be beneath a protagonist with a strong moral compass.
And on the other end of the spectrum are the stories where villains are sniveling, hopeless fools who have ideas above their station and clearly no chance to achieve it. From the get go, it's immediately clear that the antagonist is going to fail - indeed, you often feel that even if the protagonist were completely absent, the antagonist would fail anyway because their plans would implode on their own accord, from classic reasons such as incompetent henchmen who bungle everything to simply not having the resources. It's true: how many stories have you known where the protagonist accidentally helped these antagonists out in a bank robbery or launching a missile?
Of course the problem with this approach is immediately apparent: a victory for the protagonist is clear to see from the beginning, so why should the audience bother reading or watching on if there are no obstacles to overcome or tension to push against? An example that springs to mind is Mossflower by Brian Jacques: Tsarmina may seem to be a wicked and intelligent foe at first but she is thwarted time and again by nearly everyone she comes into contact with, even the lowly woodland folk. Her henchmen are beyond useless, and her lieutenant must've changed at least five times because they kept getting killed - in the space of this one book.
And this leads on to another problem: we are hard-wired to feel sorry and sympathize with those who have it tough, and dislike anyone who exacerbates that. By the end of Mossflower I actually felt a bit sorry for Tsarmina, who had to put up with a staggering level of incompetence and grief. I swear she was suffering from PTSD by the end. On the flipside, this made the heroes, especially Martin the Warrior, seem self-righteous, pompous and cold by comparison.
This kind of useless, bumbling antagonist who has absolutely no advantage on the protagonist whatsoever is quite an old-fashioned style, which is why the modern audience doesn't have as many examples of it to pull upon (Mossflower was published in 1988). The message was quite clear: being a villain doesn't pay, isn't fun, and has no redeeming features whatsoever.
But over time we saw what I like to call 'Stakes Creep' (which I'll elaborate on next week), resulting in villains that are actually so insurmountable that defeating them is literally unbelievable.
The simple fact is that the heroes should meet their match in the villain, not an unclimbable wall. Even if you do want to have an all-powerful antagonist, there should be at least a proxy that the heroes can be at odds with on a face-to-face basis and feel that they keep each other on their toes. In Brandon Sanderson's Mistborn series, omni-powerful villain Lord Ruler is served by proxies in the form of Inquisitors, who aren't as powerful as the Lord Ruler but certainly give Kelsier, Vin and crew something to worry about.
Protagonists and antagonists who can square up to one another and fight fair makes for a more honest and meaningful fight, and the end result more believable and satisfying.