A- Executing minions is easier with Smite. Tribute allows an execution below 200/240/400 Health. Smite allows you to gain tribute when minions have 350+X per level Health. This means from the beginning, you can secure tribute much more easily.
B- Exhaust is great- I admit that. But, when I observe the trade-offs, Smite is a viable choice.
C- If I wanted, I could steal enemy Blue/Red buff. They've used their Smite on the first camp, so I can just wait for the Blue/Red to have low enough health. This seriously disrupts the enemy Jungle without having to interrupt the farming of your Jungler.
D- I am late to lane. However, my ADC always makes first minion wave, and doesn't have to share exp with me. As long as the ADC plays safely, s/he can level up swiftly. My ADC is 2 when I get to lane, enemies are 1 reaching 2. And Alistar is a good enough champ to survive one level difference. And I usually force the enemies out of lane soon enough to make up for experience. Especially because they exhaust themselves trying to take advantage of a low level support.
E- Raptors gives me vision denial. Wolves gives us vision- and that vision travels a set path regardless of whose smiting it. Krugs gives me the ability to land a stun every 5/6th AA which equals CC- good for support. Gromp gives a small reward to tanking, which helps in team fights.
F- I will steal enemy jungle buffs all game- the enemy Jungle won't be out levelling me once they start ganks and I know which camps are there to take. Once the enemy jungle gets to camps- I've already cleared them. Counter-jungling.. you say Junglers dont even do it anymore- which isnt entirely true, yet even if it was- then allowing the support to do it makes perfect sense. Counter play is an amazing tool.