As an impulsive question, yours is quite understandable.
The answer isn't as simple however - the issue isn't that I can't have goblin archers or whatever, but that most heavy hitters in the MM are only heavy-hitting in melee.
My problem is that denying monsters melee is too good of a tactic. My solution is to reduce a party's ability to do that.
Since my theory is that the main way characters accomplish this is by having "great range" (that is, being highly mobile, having good "reach" or both) my suggestions focus on reducing the "range" of characters.
Why do I put words like "range" and "reach" within quotes? Because reach normally means melee reach. Here I'm expanding the concept to include, say, a crossbow archer with Sharpshooter and Crossbow Expert feats, since
he is effectively similar to a dual wielding shortsword melee fighter only that his reach isn't 5 feet, its 120 feet.
Yes - the rules allow characters to effectively slash someone with a shortsword from over a hundred feet away. No moving, no magic, no trickery
Either that, or your character has an effective Speed close to 120. That works too.
In both cases, the characters have a "threat range" where they can effectively engage monsters at distances far greater than any designer foresaw.
It completely breaks the entire MM (goblin archers notwithstanding) and it completely breaks the fundamentals of the fantasy genre D&D is squarely placed in.
To fix this, I am attempting to go straight to the fundamentals.
My observation is that with slow dwarfs with axes, the game suffers from none of these issues. Why?
Because his range is much more in line with the game's fundamental expectations. His range isn't 120 feet, it's 25 feet.
The difference is staggering.
So. The question becomes: how do we tweak the rules to encourage minmaxers* to build short-range characters?
*) plenty of people already play axe dwarves, and that's perfectly alright. I'm just identifying that it doesn't cost you enough to play a vastly more effective build using range, and so this is mostly an issue for us with minmaxing players.
I hope this answers your question; that no, it's not just a matter of having more goblin archers