I just finished all the available trials together in one go, and find that all the primal (HM) fight has much better design in comparison to (EX) version.
(HM) has more random element, while (EX) is scripted on everything. Since I m basically over-geared all of those fights already, I just play them for pure enjoyment only. From all the available one, only titan (EX), and Leviathan (EX) that seem to be more fun than (HM) imo. The worst EX is Moggle (EX), since the (HM) one has the best design, but short life, and (EX) version reduce the variety of ability moggle can use which turn the content into only hp controlling, which is more annoying rather than challenging or fun.
Ifrit : The HM version has him upgrade for 3 times, comparing to the EX version that only upgrade once and do the same over and over. The plume and eruption of the HM are actually to be interrupted, so they are harder to dodge than EX version which is good, because the EX version is nothing but simply unforgiven mechanic that is planed all ahead. While the HM one has some random part of the available safe spot each time he use too (on this side or on that side), unlike the EX one where you simply already remembered the spot, .. you can even go to stay there ahead before he use it.. And, I don't think adding a bomb on one healer and switching between them so that you can not stay near healer make content become more fun at all.
Garuda : I think this fight is basically a nerf version of the 1.0 HM, but give effect to green and red garuda which is cool. The HM version have her warp to different place at the first half which require party to check her position and run to hide, (despite there is still fix available spot she can appear on it) whereas the EX version is all the same. You know she will appear at that spot, and you must hide in the stone even before she appear, which doesn't make sense at all. Even though, she appear and only begin WS a few sec later, you are required to hide behind the stone before she attack. So basically, it is just simply forcing players to remember the spot first or watched video ahead, and here it come to why people are so complaining much about how they need to watch video ahead. You see, some content SE even require you to remember their action script ahead, so no matter how much skill you have, getting in without knowledge of fight is impossible. The debuff place on tank is really nothing other than simply an excuse that you want players to have two tanks in their part. And this is the same to every EX fights.
Titan : To be honest, I love the fight much more in HM while it was still hard in the past, but I m not sure which part of the content they nerf nowadays or simply players are over geared now. The HM fight today I had was simply boring one where no challenge exist at all. I find that the weight of earth is so slow casting now, and so does the landslide. So in this case, despite I hate for the battle to be 100% scripted as EX mode, I have to admit that EX version is much more entertaining. If I remember correctly, Yoshida admit that he made it all in script without random in order to allow players with lag to dodge little ahead of time. So he has his reason to do so here, but I still think that this is the only battle that deserved to be fully script, other primal EX should not be at all, since the pace of battle isn't this tight. (However, to me, I would be okay too if they make EX also random, more fun that way.)
Moggle : The HM version start with slow music, then the music pace become faster and faster to tell players to hurry and kill them before they summon their king. This is very good part of the fights, where you introduce each little moggle and show their abilities, why cut this off from EX? Then it was really impressed me in the first time when I heard the moggle singing their song at the second half of the battle in 1.0. I believe that a lot of people also has good impression when they hear this in 2.1 too. In EX version, the king appear since the beginning, and those little moggle has lose some of their ability from HM version, which I don't know why SE want to reduce their variety on this? EX supposed to be all harder anyway. The focus of the battle totally change from the HM that ask players to deal with variety of moggle ability and kill them into something about HP check and try to make them lowest possible. Tank duty become nothing in this fight other than swap around and find the place to stay. Basically, this fight in v1.0 was the best. Challenge, hard and fun. 2.0 make it simplier, less variety, easier, but still good. EX version of this battle is totally different and bad design in my opinion.
Leviathan : I think SE design this battle based on idea of EX mode since the beginning, so the HM is really nothing nothing at all. I can see that they probably not even spent much time on it, because they expect players to just simply skip over, unlike the first three primals HM which were good design and they probably spent more time to design those compare to their EX version. So far, I enjoy this battle, and this music. I hope that Ramuh EX battle will also be no less than this.
Ultima Weapon & Odin : No comment on these one since they never have EX version.
Overall, if SE plan to make primal weapon glow and stronger anyway, I would like to see an untune version of EX primal that you make them random their attack, and reward the item that you could obtain by the mean of synthesis please. It would really be nice.