I didn't know Tim was considered a
Sue.
The thing with Tim is that writers keep telling us he's smart. This is repeated at constantly and often at the expense of other characters.
yes Tim is used to make other's look incompetent. Case in point BRE. jason and Tim sharing a panel was at Jason's expense.
The fact that since Tim was introduced Dick Grayson's detective abilities were focused on less while they writer told us that Tim was the smart Robin, the great detective who would one day surpass Bruce. They kept telling us this with out showing us these impressive feats.
That infamous panel where bruce is talking about the Robins
I should point out that most of the hyping of Tim as the smart one or how he would surpass bruce one day were all before Damian and Duke showed up.
And upped the Ante. Sadly writers tend to use the characters to prop others far too much. Robins get upgraded with each new addition or at least writers like to go one set further with each Robin.
Damian a chid prodigy to Duke a genius meta. Not sure what skills Jarro has but he's a Starfish from space.
Like in the Robin 80th where Tynion had Dick Grayson say that Tim is smarter than him. WTF. It's the Guys 80th and not only does he have to share his anniversary with others, he's also made to say how much smarter another Robin is.
I honestly haven't seen folks call
Tim a Sue that's normally Bruce and Damian that get accused of that.
Tynion's Tim did get roasted for his nonsensical hacks.
There are those who complained about Tim fans insisting that Tim is the smartest or the best detective/only one that Ra's called Detective aside from Bruce [both false] but I've never seen anyone complain that he is a sue.
Bland yes. Sue not so much and certainly not the smartest. Not by a long shot.
People who call Tim a sue or the smart one clearly don't read a lot of comics [or stopped reading in the 90's]
Note Mary Sue doesn't mean exceptionally skilled, good at everything or OP. Other factors can contribute to sueness