Yes, they can be played in other roles, but those are extremely isolated instances. Almost always the 3 of them will be played as the support so it makes more sense to have them listed there.
This Is Your Dad2 votesI think the difference between those and say, braum, is that Braum has a kit for supporting exclusively. Leona and Alistar, while played more support than anywhere, offer up much more CC and their role is less supportive in teamplay and more tanky cc disruption. They don't actively save adcs like tahm and braum can. They lock down or disengage but offer very little else in terms of buffs or debuffs. That's sort of why nunu is a support, because he has an attack speed steroid and a slow on his e that also slows attack speed.
JavelinJoe1 votesBraum and Tahm Kench are both very tanky, and offer about as much cc as Alistar and Leona. Blitz offers a Large AOE silence, Alistar heals everything, and Leona offers increased damage with her passive.
But the bigger thing though here is that no one cares as much as to what "technical term" they are classified as. They care more about where they are played in this case. And having them as tanks and not support, means that all of the supports are not all on the same page, even though 99.99999% of games played they will be a support in the support role. If they wanted to change the name to Utility or Control or whatever, then I could understand, but Support is primarily seen as a designated role.
This Is Your Dad1 votesChampions like Naut can be played elsewhere. I think the common theme is buffing your adc or offering a shield as support in some way. Much like morgana and lux being "supports" but mages, alistar and blitz offer only CC, though his heal passive can technically be unreliable support. CC isn't what makes a "support" as they'd classify it. Braum can block almost anything with his shield and buffs both him and his adc with his w. Tahm swallows his adc and can also transport teammates around the map.
B00B001 votesthere on the tank tab because they are tanks.
JavelinJoe1 votesso Braum, Taric, and Tahm Kench are not tanky?
Death by Glamour1 votesTaric is a warden enchanter hybrid.
I don't know if this has anything to do with it but blitz and Leona were intended to be toplaners once upon a time
JavelinJoe1 votesI don't know if this has anything to do with it but blitz and Leona were intended to be top laners once upon a time
That probably has everything to do with it. RIOT loves using the old original intentions to define their champions it seems lol.
Wolfess1 votesmore like they should let us customize the tabs or make custom ones of our own aside from the default ones.
yes riot, we like being able to make customized stuff, it makes the client feel more personalized and awesome to us.
Jeddy0171 votesPersonally, I would prefer if we could make our own tabs in the champ select screen. Giving players the option to sort the champs into specific catergories like roles, favorites, factions etc.
This way you could make your own support tab that include anyone you would consider as a support.