Tibbers is unfairly the best "summon" in the game.
I don't wanna start some long rant about why im typing this so im gonna jump right into it. TL;DR at bottom

Now, I listed the champions with "summons" and pay extra note to the " " cause I know some may not be considered summon like wukong W or Sion passive etc. but I didn't want to leave anything out for this
Let's start with:
his turrets, while probably on the more annoying side to deal with are NOT even slightly meaningful individually it's only when 3 are down that they become a threat. His R turret doesn't do much either "ON ITS OWN" it's only when you have a huge minion wave + other turrets around that you see how deadly it can be due to its harder to remove HP bar. Yes, they stay around a few seconds after he dies but usually you can just move from them since they're static
Illaoi's tentacles don't move and don't attack unless she makes them (outside of E ofc) and they're insanely easy to dodge once you grab boots (swifties op) not much needs to be said about how trash tier of a summon these are as they're free gold for the enemy a lot of times
Im skipping Ivern because she's a big comparison to Tibbers and with Leblanc her clone while it CAN fool some people, does no damage it's just a prop making it only good for mindgames and not else. It's a low tier summon by far
His voidlings while great are like heimer turrets(and yorick coming later mentioning) are bad on their own and require malz E to even be even remotely functional, granted when they work, they work. Still though individually they don't do much and they don't go very far from malz without is E
His "summon" is one of the higher tier "summons" in the game. Getting dragon or the soul of a fed enemy is great. There are draw backs though. Dragon does not teleport making it limit your map pressure as he has to slowly fly over to target location (This use to be the case I COULD be wrong and he may teleport now i'm not 100% sure) stealing an enemy while great can just be a waste of an ult if you dont steal a meaningful target. Still one of the better "summons" in the game.
Excuse if I seem salty/biased as Shaco is my main. His ult is a mid-tier summon (mainly due to it's issues and clunkiness) it does damage, it does teleport and it does proc on hit effects. It's good. Then there's the issue a lot of AI controlled things suffer from. You walk into a bush and it loses any purpose and just stands there till you re-assign it a task. I hate when i'm in a 1v1 duel and the enemy goes into a bush and the clone just stands there it's irritating. Then there's the issue of the clone NOT DOING ANYTHING when Shaco dies. If it loses vision it will stand there being a free 50G for the enemy. If he had a few of his issues worked out it'd be a top tier "summon"
I won't say much about other than him being a low tier "summon" it's just too easy to escape his passive and it dies off too fast even with his steroid ability during death you won't really catch anything. Just CC it once and it's out of your hair or even slow it by 1%
Like sion won't say much as it's just not even useful it serves more of a LB passive purpose of just mindgames nothing more Wukong's clone is a trash "summon"
The ghouls dont need much say other than it's the same as malz when you land that E and W then they're godly but if you miss it's just free gold for the enemy they do nothing. Now the maiden is another mid-tier summon. Why? Because unless again you land the E and W she will ignore your target (unless they're dumb enough to fight you with no other targets around) She's great don't get me wrong but again, she has no target priority without his E being landed and dies way too fast. She's just not doing enough outside of being a great help with splitpush and soley 1v1 situations (no minions/monsters/allies etc. around)
Zyra I won't say much about because I don't play her much/against her enough to get any say-so about her plants. I do know I underestimate them a LOT and tend to get killed by them more than I should. I'm going to say mid-tier "summon" just for the sake of keeping it average
Now here's where I get into the good stuff. Daisy. She's a fun lil companion to have around knocking people up. She does decent damage and can be a big help in fights, but still a mid-tier "summon". Why's Daisy mid-tier but someone like Morde got high-tier? Daisy has too many restrictions is why. She's too slow without the enemy being slowed down (or in the middle of a fight) she won't touch them. She has a range restriction and doesn't teleport( the restriction is a reallly small range too for a "summon" she dies instantly as he dies with 0 death effects. She can't attack inhibitors. She does too little damage to towers/epic monsters. Is Daisy Tanky? Yes. Is her knockup useful? Yes, but her restrictions are still too much to use in a situation where both teams are competitive. I'm not calling her bad by any means I am saying she's too limited for real use.
Then finally we have this btch of a bear. Most if not all other summons i've stated had restrictions that gave them a weakness/counterplay measure. What's Tibbers? (Before anybody says his cast range i'm talking about the bear itself) He comes out with burst damage, he does continuous damage to enemies around him, he does damage through autos, he's by far the fastest "summon" (unless you build a ton of MS on Shaco I guess for his clone) he doesn't die when Annie dies and instead gets a MS/AS steroid. He's pretty tanky for a "summon" and to wrap it all up (forgot to mention this for daisy as well) the cooldown is already counting down as he's summoned instead of after he dies (which happens for yorick I believe someone correct me if i'm wrong) Tibbers does FAR too much compared to any other "summon" in the game and has far too little restrictions. It's not fair in the slightest.
TL;DR: Tibbers does FAR too much compared to any other "summon" in the game and has far too little restrictions. It's not fair in the slightest. Compare it with any other "summon" yourselves