(I am aware that there is information about Ultimate that has been leaked, and some of it would be relevant here. However, in order to avoid being spoiled on the game I have avoided watching any livestreams or info dumps. If there is relevant information that affects this post, comment it, or tweet me @amiibomd.)
If Spirits are allowed, the Improved Escapability bonus will probably ruin the meta, unless previously unknown information comes to light. Improved Escapability singlehandedly counters an entire class of amiibo, the Grab class, making the only viable options Defense and Attack. The fact that it does this by taking up only a single bonus effect slot spells D-O-O-M for anyone using the Grab class. As we witnessed in the Smash 4 metagame, the Critical Hit bonus crushes any defensive resistance that may await it, not to mention the newly uncovered Special Move Up bonus. An Attack-based amiibo with Improved Escapability counters Grab amiibo, but if he has one of those bonuses then he also counters Defense amiibo.
Defense, meanwhile, only has one effective ally to its name: Explosive Perfect Shield. While Explosive Perfect Shield is indeed quite overpowered in Smash 4, to the point of banning, that doesn’t mean the Defense class will have much of a leg to stand on. Even if Explosive Perfect Shield is allowed, how are Defense amiibo going to get KOs? They’re not supposed to attack! As we saw with Smash 4, when Defense and Attack strategies fight, Attack wins. Little Mac and Cloud demonstrated that quite well-you’ll notice no amiibo were ever banned for being too defensive.
This may have its benefits: it could encourage the amiibo scene to become offense-based. Smash 4’s defense-based metagame was terribly boring, and probably led to the downfall of the scene (aside from other, non-amiibo reasons). It could also keep the metagame from staling out, especially as new amiibo are released with new attacks. Defense-based metagames tend to burn out, while offense-based ones last longer. Anyone who’s played on 2Fort knows how two opponents using a defensive strategy will play out.
Unfortunately, the game’s physics don’t seem to lend themselves to offensive amiibo training. While it is certainly faster than Smash 4, the changes to perfect shielding seem to indicate that defense is still the superior option. A character that perfect shields an aerial attack stuns the attacker in midair, allowing him a short window of time in which to counterattack. The opponent, meanwhile, can only stand and take the attack.
In Smash 4, amiibo could perfect shield… perfectly. Any attack was immediately counterattacked, which resulted in (to my dismay) a ground-based, defense-based metagame that was pushed ever harder by the elimination of all non-flat stages. In Ultimate, the problem does not seem to be solved: while perfect shielding now occurs at the end of the attack, if amiibo can still be taught to consistently perfect shield then the ground-based metagame reigns supreme, favoring amiibo that have quick attacks usable out of shield. Both amiibo would have to learn to stay on the ground in order to avoid having an attack perfect shielded.
“But wait, there’s a solution! We can just have our amiibo grab their opponents!” You might say. And you would be right, if not for the Improved Escapability bonus. Now we are back at square one.
There are a few ways out of this loop, including but not limited to:
We may have a bonus that negates the Improved Escapability bonus, or the Improved Escapability bonus could be significantly nerfed from Smash 4.
The Grab stat could overwhelm the bonus.
Amiibo may not be able to perfect shield often, if at all. Command grabs could ignore the bonus and rise to prominence.
A Neutral amiibo may be better than all three options.
With all that being said, unless there are some wild cards that have yet to be seen (which is possible), we need to operate under the assumption that bonuses should continue to be disallowed in amiibo competition. Whenever you allow for a variety of concrete options in a metagame, there will always be a dominating choice. It looks like Improved Escapbility is that choice.