Higher legendaries capture rate with excellent throws?

Just educate yourself a bit on probability and you will understand. Excellent throws increase your chance to capture a pokemon but for the medium experienced player it’s usually advisable to go for consistent great throws instead.

https://pokemongo.gamepress.gg/raidcalc#/

Use this a few times and you will see that the catch chance difference between "small circle" great (~14% per throw) and excellent (~15% per throw) can be minimal.

So even with excellents throws + golden raspberry (+gold medals) ~85% of the times the legendary pokemon will break free, at every throw
(Ray, Groudon, Kyogre, 2%base catch rate).

If you can consistently do it I am still a firm believer that excellent throws are the best, given that they have fixed the curve ball bug.

That being said anecdotally I have terrible luck on groudon and tyranitar (scoring mostly excellents), but I have slightly better luck on Zapdos, Kyogre and Rayquaza (scoring mostly greats).

The few near misses on the excellents may have costed me though, for groudon and ttar.

I've never hit (or tried to hit) an excellent on kyogre and I am 24/32. I hit all 90% excellents for Groudon and I am 18/28. Hit mostly greats for Ray and I'm 14/17.

I went for great throws in Kyogre Raids: 64,8% catch rate
I went for excellent throws in Ray Raids: 84,6% catch rate

So yes: Go for excellent throws and don't let probability fool you!

This is completely anecdotal with no factual basis but I seem to have more luck firing off quick Great curves instead of slow, patient Excellent throws. I like to think that taking too long to throw gives the Boss a chance to reinvigorate itself. In reality i'm just not good at throwing Excellents.

I can certainly relate to this. Threw about 20 excellent curve balls with golden razz to start Suicune off without any luck. Then caught my first one with my very first great throw. Go figure.

Is it rayquaza? I'm pretty sure rayquaza is incredibly resistant to excellent throws regardless of who tells you otherwise.