Some of these optional bosses are boring the heck out of me

[Pete for President]

Ah yes, but on those occasions when they pull them both out... then it's not strategic. It's cheap and it's lazy.

I don't see how it's really any diffrent from a barrier change boss or bosses with invincibility modes and nasty counters like Guard Scorpion, Ymir, and the Mist Dragon.

I mean all the boss does is throw a monkey wrench into the players rhythm and strategy by becoming temporarily invulnerable and forcing you to go on the defensive. It's still the same principle concept as the bosses I listed above. It would be cheap and lazy if the boss used this time to say... restore all it's health, but they don't do that, they just change the flow of battle. A lazy boss is the Oblitzerator from FFX, who would be a challenging fight, especially at that early stage in the game but instead, the game makes the fight completely pointless by having the party telegraph the strategy for beating it, and said strategy cripples the boss to the point it losses most of it's health and can perform no action, making victory guaranteed. That's a lazy design boss fight because why would should you bother if the designer is just going to give the win to the player anyway?

The Palings work, because they force the player to change their own strategy and upset their rhythm, so I would argue its a good thing because it forces the player to react instead of just "hit it til it goes down". Yiazmat is probably more of a real argument for a lazy boss fight design since it's more of an endurance match than one that requires real strategy.

The thing is, the palings feel totally out of place as a random way to gain invincibility. Where's the creativity in saying; oh I have a paling now so I'm invincible. And yes, I did pull it out of my ass.

Some random examples of how they could have generated the same effect without a lame trick:
Want invincibility against melee? Make the boss fly out of reach from swords, cover up in a shell, make him hold a big ass shield. Invincibility against magic? Silence the party, dig underground, cover yourself up in element-resistant scales, or eat the magic for all I care. That way it makes sense for someone to change strategy, as there is a logical, fitting reason why a certain tactic isn't working. It gets the environment involved and makes use of the boss's unique characteristics.

That's how I feel about it anyway. Reminds of how simple but sophisticated Vagrant Story's bosses are.