Fonseca happened...
Yes, Fonseca seemed stagnant, I even thought he made some steps backwards, but... Among the results there are the Davis and Laver cup matches, against high ranked opponents. And I do think that he and his team are actively adapting his game, hence the strange matches.
Also, waiting to pounce on the very last bit of the season was a smart move. I guess even winning the title he will go full steam to Paris, specially given his first round opponent.
Yeah, I think he was consolidating, adjusting to the limelight and the rhythm of the tour. The talent is there to be great, even if we're not yet seeing it in results beyond a match here and there. This is also why I don't rely entirely on age-related accomplishments (i.e. X rank or Y title by Z age). That stuff is a good starting point, but ultimately it comes down to their talent - and this is where I always balance that analysis with the eyeball test and listening to what people who have a sense of such things are saying. In a way, it is sort of 50-50 (for me): statistical thresholds and talent assessment. I focus on the latter because I can do it, and mostly rely on others for the latter, whether Gill Gross and Andy Roddick, or my friends here.
I think of players who rated well in the former but never amounted to much: Coric and Tomic come to mind, but there are many others. I don't remember many people seeing either as future stars - it is just that they appeared on the radar at a very young age (Kyrgios, who was a bit older than Coric but showed up on the radar around the same time, was a bit more promising). For awhile, both were the youngest player in the top 100. Tomic had that impressive run at Wimbledon in 2011 at 18 that made everyone pay attention, then he plateaued around #50 for a few years ago before surging into the top 20 in 2015. By then, though, he was already 22-23, and players who first enter the top 20 at that age literally
never become greats, and only a few end up as elites. That's where the threshold analysis is useful.
For Coric, it wasn't as much a particular tournament or win as it was that he snuck into the top 100 at 17, just before his 18th birthday - largely on account of a Challenger title. He finished 102, then kept rising with solid play as an 18-year old, reaching as high as #33 before finishing 2015 at #44. Meaning, his 2015 was similar to Fonseca's, at least in terms of overall performance and age. Probably Coric's signature win that season was beating Andy Murray in the SF of Dubai, though got crushed by Roger in the final. Anyhow, I remember people talking about him having limited upside due to a lack of weapons. That turned out to be totally true, although Coric did end up improbably winning the Cincinnati Masters in 2022.
All of this is my long-winded way of reiterating the point: rising in the ranks at a very young age is an important start to displaying potential future greatness (or eliteness), but it can sometimes be relatively empty. By the eyeball test, Tomic was probably a bit more impressive than Coric, but neither really wowed anyone with their talent (iirc).
One final note about Fonseca. One reason I'm not too worried about his seeming stagnancy is that I think we tend to be somewhat jaded and think that it is "Alcaraz-Nadal or bust." Sinner took awhile to fully mature - showing steady growth (and a bit of backsliding in 2022) before really showing us what he was in late 2023, around his 22nd birthday. Roger's rise was slow relative to other greats. Even Rafa spent a couple years in the middle of the top 100 before surging. Or we could look at Pete Sampras, who did breakout as an elite at a young age (1990, or 18-19) but took a couple of seasons in the back-end of the top 100 to surge, and then after winning the 1990 US Open, took almost three more years to win his next Slam. Fonseca is still very young - and really, he's a young 19 in terms of how much he's played - this is really his first full year on tour. In a way, I think the flashes of peak moments are more important than consistency, which will come as he gets used to the grind of the tour.
2026 should be a lot of fun to watch. If people haven't taken note of Fonseca yet, I think they will next year. I think a reasonable expectation is that he breaks into the top 20 (maybe top 10, but I'll see that as a bonus), and wins a few titles (maybe a Masters, but again - that's a bonus). I think he'll go deep at some big tournaments, though I don't expect him to be a regular contender at most until 2027. But we shall see!