My opinions on Exhaust and Heal
Exhaust on Support and Heal on ADC has been quite a trend now since the Heal changes long time ago, which made ADCs move from Barrier to Heal. Although I think that the trend should change again, swapping these summoner spells for these roles.
Heal 
on Supports
Every ADC right now uses this summoner spell, my opinion should be, that it is a better spell to use as a Support.
What it provides: More heals, resulting in more protection, your own protection since you are a squishy target that will be focused more than the ADC in teamfights, especially if you are playing Soraka/Sona etc. Supports have long cooldowns and high mana costs, this summoner spell + the Insight and Windspeaker's Blessing + Ionian Boots of Lucidity masteries could interact really well.
Heal's base cooldown is_ 240s_ (4 minutes). With Insight and Ionian Boots of Lucidity it is reduced to_ 180s_ (3 minutes).
Base healing to 90-345. With Windspeaker's Blessing it is increased by 10% resulting in bonus 9 and 34.5 on max. Adding +30% more healing power from Mikael's Crucible and Ardent Censer, resulting in 40% which is min 90 (+36 bonus) and max 345 (+138 bonus) healing. It is worth to note that it gives 30% bonus movement speed, which can be used to boost allies up (e.g Heal + Lulu's Polymporh) and it will provide 5 to 22 armor + 2.5 to 11 magic resist thanks to Windspeaker's blessing. Heal's summoner spell value is also increased by Ardent Censer since it can provide bonus attack speed and magic damage on-hit, resulting into an awesome summoner spell for support.
Heal will also provide survivability for supports since ADCs have Life Steal, it will provide more protecting power, since a lot of ADCs use Heal for themselves as they fight solo.
tl;dr - I think Heal is a better summoner spell on Supports since it can be boosted by various masteries and items that support use more often.
Exhaust 
on ADCs
ADCs are frequently left in lane lone, the Support is respawing/shopping; or warding the river; or ganking or; collecting chimes.
They are frequently bursted down by Assassins (Rengar, Katarina, LeBlanc, Shaco), and this is where Exhaust comes in. Exhaust reduces armor/mr, damage dealt and mov/attack speed. Since ADCs are the ones getting bursted, and the supports are usually far away or somewhere else, they can use Exhaust in their advantage and more likely survive, than waste a Heal on themselves.
Didn't have much to write here as I wasted my time typing about Heal and forgot what I wanted to say about Exhaust ;-;
Tell me your thoughts or opinions on this.
Thank you for your time.
Sincerely, a player with no main
