As a long time supp main I'm not here to agree or disagree but there are factors to the lane.
Yes mages are being played in the botlane..I've suffered Malz..Brand Annie YOU NAME IT, I've seen it and had to deal with it.
So maybe I can maybe give some tips/tricks.
Brand is being picked alot ( I tend to ban him cus I hate the poke+free ignite) Sona Roka and Nami help keeping your adc alive. Suss=Poke=Longer in lane.
I cannot stress this enough.. READ YOUR ENEMY LANERS. What I mean by this is read their actions, if they're going hard af on you in early lvls use that to your advantage! This means their supp will be blowing mana and possibly a few sums at lvl 3, Com this with your jungler. If they're agro af play more safe, and look for a opening to make a play. Most of the time a agro mage supp like Brand is all kill hungry and will separate from their adc JUST to try and land some spicy kills. With this being said, if that player/players are in that mindset you can use it against them. Coordinate with your jungler. EX " Hey so ___ flashed WEQ, adc was farming we can Iso him and pick up a kill bot". Now if you jgler is braindead you can try to coordinate with your adc or mid laner as well.
Synergy is important in the botlane as supp players you should know this, and if you can see the Ops lane has zero use that!
If you are recalling please take this time to look at other lanes and try to read what the enemy team plays like, so you can use this later on.
Now for the main complaint "Mage or gamble" do you have to play a mage in the botlane to win? Nope..I like people with hard CC..Like Leona Hard AP team build MR Heavy AD..Build Armor. And Just in case someone asks I take Coin over relic cus I cant depend on adcs letting me hit that spicy minion for my supp item.
I also adjust my play style to what the enemy team has picked...FOR INSTANCE- I pick Roka..I see a Zed Garen Jinx Brand Uydr. I swap my runes to tank and play Roka tank vs AP. Get my Ardent then full Warmog tank cus My Hp/Regen=More juicy team heals= I stay alive longer.
Hell I even play Karma as a tank..nothing more fun then running up in their face taking all the skill shots and still locking them down and getting out with 40 hp and my team picks up a double kill.
IT MAY NOT BE META but it works. And play what you feel comfortable with cus your knowledge of a champ will always help you over someone who got auto filled and is picking the most "OP" shite atm.
AND sometimes..no matter how hard we try as a support and how smart we are...We CANNOT help stupid. Just keep that in mind <3