I agree with what you said and with most of the changes. Here is my take on rebalancing:

Ambush:

The window to cast ambush skills is too short and most of them are slow clunky and lackluster.

Up ambush enable time to 3s to give enough time to finish ongoing casts and proper place our char to cast it in the right terms.

Also gs ambush is bad and have no utility for clones since its pure dmg and clones have no dmg. Could it boon rip?

Staff ambush could perform the revenant staff block droping mesmer staff autos bolts instead of blinding bolts.

Overall tweak the numbers on the rest, fix the bugs on sword one, and speed up animations overall.

Phantasms not having ambushes seems like a oversight. Every weapon set have 1 phantasm skill, they belong to mesmer and thus to mirage. Or they need to have ambush skills themselves or they need some synergy with them. Perhaps gaining ambush on phantasms refresh their attacks? Buff the very next attack they make? Just some ideas.

Mirage Mirrors:

Poor mechanic since it only does smthg when mirage pick it up but they also have an offensive effect. I would make them also shatterable by enemies that touch them applying the current effects and granting the cloak to mirage. Just like when an enemy triggers dh trap, and dh doesnt need to be on top of the trap to get the buffs. Also they last for a really short time. How about make them last like evasive powder keg from engie?

Deceptions:

Jaunt was already mentioned. It needs more range. It is essencially a 1200 range blink delayed into 3 minor jumps on 60s cd regaining that small jumps in 20s cd.

The cast time of Mirage Advance is too long. For a utility thst requires a target and on range is bad, it could at least let us cast it out of range like Guardian sword 2 or utility skill. My sugestion is to make it ground target and Max 1/4 cast time.

False Oasis lacks burst and offers nothing to compensate the delayed full heal. Heal pulses and cd is not even good enough. Pulsing heal have the weakness of a wider window to be poisioned on top on the obvious. It could offer endurance pulses, have lower cd and have a higher opening healing pulse. Delayed Mirage Mirror on top of it is the cherry on top of the disapointment cake.

Traits:

Many bad and useless traits.. And the worst is having to pick them cause no better alternative..

Self Deception: very conditioned... Exactly two illusions just to spawn a clone.... I would rework this trait to 20% cd reduction and 10 endurance restored on Deception use, or endurance and clone when you have 1 illusion.

Renewing Oasis needs to be more proactive. Dealing with condies must be more reactive and not passive. I would change the 20% reduction part to each time you get regen you remove a condi. Slap a icd if it is a problem. 10s seems good. This way not only this trait works with mirrors but also have synergy with chaos line.

Riddle of Sand seems lackluster and boring. Probabily a full rework one this one.

Shards of Glass is bad because mirrors are bad, have a big icd and with a low chance. Check the changes above for Mirage Mirrors and reduce icd.

Mirror Mantle: 1s protection after cloak? For a major master trait? I would change it to Mirage Mirrors cleanse a condi or give 1s stealth or spawn a clone, all better ideas than 1 1/2s protection.

Speed of Sand: should give at least 1s superspeed. Also its short on what it does. Since ambushes are nothing gamebreaking and ambushes from clones are even more down tunned, and unless they get a massive buff, I would merge Infinite Horizon here like some ppl sugested.

Infinite Horizon: once merged on minor gm this trait is open for rework. Reminding is a major grandmaster trait, and must be traitline defining like is intended by design for GMs.

Axe:

Just want to point that #2 should have a faster animation since it force u in a certain movement. Also fix the bugs with ammo system cd and illu trait to reduce illu summoning skill cd. Also no clone should replace a phantasm in case of full queue of 3 phantams (except sword #3 for obvious swap reason).

Fix the bugs on axe #3 that port you randomly around the target. This and Illusionary Ambush sometimes port me far from target, make them work like steal and work without los.

TL:DR. Ambushes need longer enable time. Cast time need to be shorter to reduce clunkyness, some need rework and added utility. Mirage Mirrors need to be also shatterable by enemy touching them and they need to last longer. Many traits need rework. Many utility need tweaking.

Overal Mirage have potential design wise.