For background I've mained Summoner since I started a little over a year ago, so I do not have any reference for it through its iterations.
This is mostly just from my observations and feelings, so it's just my opinion but I was curious if this rings with anyone else.
So with the new Summoner I want to start with what I like, because there's quite a bit to the rework and I just like to start with the good news. The new animations look visually stunning. It's such a pretty class to play. Also the buffs to DPS for abilities has increased the damage output amazingly. It just burns through enemy HP like a wildfire. This is mostly because everything was buffed to make up for the lack of DoTs which I think is a good trade. While I'll miss the dots the damage they'd do has been more than made up for. Also our Carbuncle can just shield us whenever which is a nice defense mechanic for immediate help instead of the previous Summon Titan-Egi and then wait for them to cast the Shield, which while nice didn't help for sudden Oh-Nos during combat.
However these boons have replaced what made a Summoner, a Summoner. Yes we have the animation of Summoning, but we don't summon anything other than a Carbuncle/Egi that can buff us or our team, only when we're not using other spells. We "Summon" our Egis/Primals to do an attack... then they leave and we have access to new spells that we cast. So by that reason it's not a Summon, it's a casting a spell to enhance our other spells. Yes we Summon Bahamut and Phoenix, but that's it now. For the most part we're just a Black Mage 2.
Before we had actual Summons that casted abilities from themselves when we told them to. They would stay with us and attack our foes. They were minor but fun and I had to choose which Summon was best for my scenario, be it Garuda for AoEs to deal with adds, Ifrit for bosses. and Titan for a more defensive play. When I chose one of their abilities it was cast from them not from me. They were an actual companion with me in combat. There was thought that went into the gameplay. Now each Egi-Cast does the exact same thing once and then leaves and just alters how quickly your spells, that you cast, attack/how much damage they do. So they really don't matter that much. It can mostly be summed up as cast as many spells that aren't on CD yet. So this fun, class that required a little thought is just mind numbingly simple and... you just cast really pretty spells while your Carbuncle(Or Egi if you changed it) does pretty much as much as a Minion since you only need it out to cast your other spells in which case it just disappears during that time.