Why not make SMN's Bahamut do Megaflare when it's summoned

[remiff]

The reason is simple, just because with the current summoner's mechanics, it wouldn't work.
If Bahamut deals more damage than Phoenix, as it was the case in 6.0, a level 70 summoner would be stronger than a level 80 summoner,
because summoning Phoenix would be a reduction in burst damage.

To implement this, you would need to separate the Bahamut/Phoenix summon buttons to give summoners the choice of whom to summon based on the situation.
For example, by introducing a 1.5-second cast time/2.5s recast for Bahamut and making it stronger than Phoenix in exchange, while keeping Phoenix as an instant cast ability and focused on support.

I don't know what they have in store for the Summoner in 7.0, but many of its mechanics will need a complete overhaul if it is to undergo fundamental changes.
The current rotation has several issues that need to be addressed in order for the future kit to be more refined than it is currently.

If the Summoner remains as it is currently, we'll likely just get different reskins of the existing Legos ''elemental-summon'' and end up with a rotation without real strategic choices, much like it is now.

In my opinion, the best approach without a complete rework would be to separate Phoenix and Bahamut, add three buttons for 3 potentials new summons, and provide three gems that can be spent on three of the six different summons of your choice.

This would involve creating three high-risk, high-damage summons and three medium-damage, mobile summons to allow summoners to consider whether it's worth taking risks to increase their DPS or if it's better to play it safe and avoid a potential KO, even at the cost of some DPS.

I also believe that Energy Drain/Siphon should be removed, and two stacks should be added to Painflare and Fester, which should theoretically be renamed since we no longer use bacteria,
they should, of course, have a shared cooldown, meaning if you use Fester, it consumes 1 stack of Painflare and vice versa.

In return, they could introduce a new resource management system with the Carbuncles, as they currently serve little purpose.
Giving them a real utility and a spell, and removing their role as receptacles for summons would make sense.

Physick should also be removed because its existence no longer makes any sense, as it is entirely useless.

It is time for them to remove useless Arcanist spells that the Summoner still shares with the Scholar because they are fundamentally two distinct jobs, even if they have the same starting foundation.