"Having the serve in singles is
a big advantage"
That is a generality that is mostly true but in some cases clearly FALSE.
Suppose you wanted to investigate the receiver advantage in doubles and you randomly chose to track Arregui when receiving from Beitia, Angel and Arrieta.
Would you say, "The RECEIVER advantage in doubles is HUGE - about 65%!!"? Of course not because the advantage is a potential only, and not an across-the-board constant for every player.
Compare the situation to tennis. Big servers at Wimbledon like 6' 1" Pete Sampras or 6' 4" Goran Ivanesivic used to win almost ALL of their service games. But if you were trying to handicap the serve percentages for 5' 2" Amanda Coetzer, 5' 5" Tracey Austin, or 5' 6" Cris Evert, you would be making a massive blunder to expect the same figures from them. The shorter and less powerful women often did better when not serving.
For Pete Sampras at Wimbledon, it was 'serve and volley'. For the elite singles players in jai-alai, it's more like 'serve and take control'. The singles serve advantage consists of those 2 parts. Problem is, the lowest echelon backcourt players in game 1 singles do not have great serves and they do not have the skill set for the 'take control' part either. At Dania, Elgezabal, Elizalde, Garita, Minte, Ibon, and Larrea generally win more points receiving than serving. I can't say anything authoritative about Miami because I haven't been able to watch closely for a few years. But when I did watch, it was the same pattern.
In addition to the lack of 'STC' skills, there is another important factor. Because the earliest singles game is effectively 'backcourt follies', many of the serves are tentative and SHORT. So Larrea, for example, on his right side, can often step up and cream the ball for an immediate pass and maybe chula / chic chac / tough rebote / weak return - if any. Advantage receiver.
Finally, let's go back to tennis and think about the second serve. Because of the loss of point penalty for a double fault, the server has to be careful and take something off of his serve. That alone can flip the serve from big advantage to big disadavantage. In fact, I just saw some stats from a Djokovic-Nadal match in Rome when Djokovic won 47% of his 2nd serve points, but Nadal only won 25%. IOW, Nadal got slaughtered on his second serve and lost the match. So if we compare the difference of mens 1st and 2nd serves in tennis - in terms of being CAREFUL - to the difference in jai-alai between elite late game front court serves vs early game backcourt serves, it is not that tough to believe that serving can be disadvantageous.
At any rate, besides the reasoning, I have the observations and statistics to back this up. But anyone who had the patience to watch and track the foot position of the receivers for game 1 / 4/ 7 / 10 / 13 would reach the same conclusion.