The latest edition of Fantasy is a bit of an enigma. It comes across much better compared to previous editions and in most respects, plays a lot better. There are however a few things which stand out. One is the randomness of a lot of aspects within the rules, specifically terrain and charges. Whilst it's pretty easy to simply ignore the terrain rules we have to wonder what they were thinking in regards to having a random amount of terrain which have random effects. Terrain in 5th edition 40k, even though there are strict guidelines, are bad enough because so many people don't follow them. When you do follow them and specifically have line of sight blocking terrain, well 40k plays a lot better. With this in mind they had a good template on which to base things and threw all semblance of order out the window. Plain odd... Random charges also really hurts. Those double 1's or combination of low numbers do come up and whilst obviously getting as close as possible minimises this, having a unit which is in charge range of your opponent 95% of the time fail to charge, well that hurts. This is mildly comparable to difficult terrain tests in 40k but as many will point out, they don't like the randomness in that either.
And then we turn to magic - specifically the 'ultmiate' spells of many of the regular lores in the rulebook. The raw ability of these spells to simply devastate whole units in single turns is staggering and this is where a lot of 8th edition can come unstuck. Not that magic can decimate units but to the extent and ease that it can and if you cannot defend against this or do the same back to your opponent, you are very likely to lose. Consider what Nikephoros points out in this post - there is a semblance of balance in terms of army composition to 'address' the power of magic. This displays itself as follows:
Magic/Warmachines > Mass units/hordes
Mass units/hordes > multiple small units (MSU)
MSU > magic/warmachines
Magic and Warmachines decimate large bodied units. Their damage is often predicated on having a lot of models to damage. Warmachines use blasts or lines to determine damage and with the block formations of Fantasy, if these hit they will cause a lot of damage. The ultimate magic spells often force models to pass tests to survive and obviously the more models that need to test, the more models which are likely to fail. There are also blast magic spells as well, particularly RIP (remain in play) spells which can run around causing damage for multiple turns. All in all, being a large unit against magic and warmachines sucks.
On the flip side, smaller units care far less. It's harder to hit them with large blasts or lines or at least hit a lot of them at once and spells which force pass or fail tests have less impact on units with less bodies. The problem with MSU units is of course their damage output and their inability to shift large units thanks to steadfast. They are also far more vulnerable to damage from conventional means such as shooting and close combat to the point where they are in effective. MSU can survive a barrage of magic and warmachine firepower great but you are vulnerable to normal shooting and need multiple units to charge at once to have any chance of breaking large units.
What this ends up being is a world of rock-paper-scissors - what people commonly believe 40k is when it's not. There are clear advantages and disadvantages for each unit type and if armies of only those unit make-ups faced each other upon the table-top, one army would have a clear advantage. If one could incorporate all of these aspects into an army list though, they would have an apparently balanced army list. Unfortunately, whilst certainly possible, this is does not seem to be the case in terms of how the game unfolds and we look back to magic as the one factor that can unhinge this.
Let's take a couple of armies as an example. Both have excellent casters which can throw dice at ultimate spells with miscast protection. Large units which do a couple roles really well. Some Warmachines backing them up to further cause damage to large opposing units and provide early ranged firepower. Scouts to movement block in early phases of the game. Both have some MSU units to give more movement options, harass warmachines, avoid massive firepower, etc. Who wins can depend a lot upon player ability of course but let's assume both players are equal in every respect. The winner is then nearly always decided upon who kills the other's mage first. Not only does this take a lot of firepower away from your opponent but it hurts their defenses against magic for the rest of the game. This means in terms of list building one doesn't really have to focus on all three aspects of the rock-paper-scissors premise but rather ensure they can eliminate their opponent's rock (magic) whilst protecting their own. By then having a weakness to paper (MSU) they can cover this with their scissors (horde units) if they can ensure their survival by eliminating the rock (magic) as early as possible or vice versa.
Now let's assume magic was less powerful. Let your imagination run wild on how this might be but let's say warmachines become the more reliable way to deal with hordes with magic acting as a supplementary force. Warmachines are a lot less reliable than high level mages with miscast protection with misfiring and artillery dice added in. Thus, whilst they are still powerful against hordes they aren't the be all and end all that magic currently is. This would still leave a rock-paper-scissors design in terms of units which is fine when they can all be incorporated into a singular army which isn't going to be rick-rolled by an army not following this principle. With the reduction in the power of the ultimate magic spells, supporting spells might see more regular use. They are certainly used currently but more often than not play a distant second fiddle to damage spells of massive power.
Regardless, if this were the case, I imagine Fantasy would be a lot more balanced. You would see the theory of taking magic/warmachines/MSU/hordes applied more readily, rather than focusing on a couple of those aspects. It would be harder to make uni-dimensional lists and do well against any list opposing you which you currently can do with massive magic ability. There would still be some issues in regards to rules (i.e. terrain, random charge distance, etc.) but there wouldn't be this one over-riding factor which can unhinge whole armies. With that in mind 8th edition Fantasy is massively better than previous incarnations - just with this massive elephant in the room. It's still fun to play but as Nike has been pointing out in his series, it really is the 'beer and pretzels' game by Games Workshop. You can play it competitively and there are a set of skills which are required to play the game well. You just have to understand there are going to be games that are lost and won simply due to magic and this can limit the competitive application of the game. It's still fun, don't get me wrong, just don't get butthurt when you lose or when someone points out the inherent imbalance within 8th edition.
