I actually had a whole long answer typed out on why I love Summoner after doing a whole tier of raiding on it this expansion since the rework and then as I was going over a cons of it I came to the realization... I actually DONT think Summoner is fun. I think it is incredibly rewarding to play at a high level and from that I get a lot of enjoyment out of it when I preform well. I very much loved Heavensward Summoner and found it to be fun in all ways. I felt the same about post rework Summoner in Stormblood. I detested Summoner in it's form before the most recent rework for Shadowbringers, but certain changes removed several frustrations I had with the class and the buffs made it so that the work you did made the effort you put in feel worth it.
But I don't get the same enjoyment of it that I did before, where I would just jump on it for just the funnies in expert and 24 man because I just WANTED to play the class, which is what I do now with Black Mage and Samurai. I raid on it because I still do like the aesthetics of the class (Phoenix for the win), I'm displeased with my old main job's changes in ShB (Bard), and the class I feel does reward me for the effort it asks for and hold a very well rounded role on any good raid static. But that doesn't = fun. The rotation still to me feels incredibly disjointed unlike 3.x and 4.x Summoner which felt like an absolute dream. It still has numerous issues with Pet AI that while I can compensate for, just makes me wish they would do away with Egi's entirely and turn to a rotation that features the Demi summons and makes them the primary feature of the job. It still feels incredibly clunky where I'm having to do things that go against my normal DPS mindset to make sure I'm getting out the most amount of Wyrmwaves and Scarlet Flames. It still is absolutely dumb that Bahamut/Phoenix still FOLLOWS ME AROUND LIKE A DAMN LOST PUPPY WHEN IT SHOULD BE EASY TO JUST MAKE IT SIT FREAKING STILL WHILE I MOVE!!!
This is of course all in the eye of the beholder. I know some people who absolutely love the job and feel it's never been better than now. But for me the constant annoyances of the class still put it in a place where I can't say I find it fun. But in it's favor none of those annoyances I find game breaking. It's not like MCH where ping makes me hate my life and not want to play it. It's not like Bard where I feel like I'm playing flight of the bumble bee and I'm getting nothing for it while other jobs sing ABC's and do more. It's not like Monk where I feel the job is conceptually just BROKEN at it's core. It just has more to do going into the next expansion to continue to clean up the mess that the initial rework caused.