[Autumn]

Currently I think that Install being main class is a bit of a fair spot for the specific reason that gaining any of the youkai's sync mind abilities can be a huge sway in the favor of the summoner, its insanely good. But most of the benefits of installing come from gaining that specific youkai's unique skills. 

I do think Install also plays an integral part in summoner gameplay sometimes, it allows the usage of Soul Chains and Two Souls Beyond (And thus installed Fight As One) in the current two summoner classes, but with the addition of a new summoner class coming up which almost surely has install in mind for its mechanics, I do think Install needs to be changed to not be main class, with a limiting perk for main classed summoners.

A while back Void Assassin's Voidveil was changed very similar to what I'm proposing, since without access to voidveil, VA was missing quite literally over half of its kit.

This specific tidbit comes into mind: 


"*You can access to all of that youkai's abilities"

If this was removed when you're not main classed summoner, this would be perfect, since the main line that separates how good install is from other main class skills is the immense versatility that comes with it, whether you have access to stat increasing effects like Radiant Roa and 777, or situational immunity/resist/absorb or even REFLECTION to a wide variety of elements.

TL;DR:
Restrict access to a youkai's unique 'install-only' abilities when you are not main class Summoner, and make Install not main-class anymore. This would not only be a likely QoL for the new class, but also be a huge QoL bonus for both Bonder and Grand Summoner.

[Raigen.Convict]

Did someone say Combination Fighter stacked with soul chains Judgement Blade?
(I like this idea, yes please)

[Senna]

This idea could work but it seems more like Fluff than anything else. I'm okay with it though. It sounds more like preparing for the incoming new class to make new class synergy.

I'm game for it.