It should be clear that even with the case of Aritz being mismatched at Miami, you don't reach those probabilities. I'm no horse expert, but here in the US, the faves are supposed to be winning about 1/3 of the time, right? So, despite those complicating factors you list, the public is able to cut right thru and ID the best horse.
Do you think that a summary of the last 10 years of jai-alai would have the tote faves winning at 33%? No way.
So if ID'ing the probable winner is not what supports "easier to handicap", what is?
Bear in mind that with respect to winning, Mr Straymar made the statement that not 1 in 100 can do it. And that, sans rebates, he might not be participating.
If you are basing your position on the ease of sniping in the largely abandoned WPS pools, that has to be regarded with a big asterisk, since scaling up beyond $2 will usually kill any wager value. It's not a fair representation of jai-alai handicapping as a whole.
So, how do we establish that jai-alai is easier to handicap?