The land was turned over to the state/county from federal government as a part of base closure act. Five Points (FP) is a special LLC formed by Lennar to develop large scale projects using private-public partnership. Lennar has others, like the project to develop Candlestick Point in SF using a similar subsidiary organzation.
When I was at the Irivne City Council meeting few years ago when they took up a vote to allow Five Points to develop the land around old El Toro MC Base. (The arrangement as you've described that FP pays for the park in exchange for being able to develop the surrounding communities in Irvine.)
The OCGP does not have all the restrictions of Irvine parks in that there is no requirement for certain percentage of Irvine residents, in order to gain access. You just have to be OC resident, as the park actually belongs to the county and not the city. It is maintained by the city under the county contract, I'v been told.
Since OCGP is a showcase place for county and they view it, much like how Grand Park is viewed in Westfield IN, its highly unlikely that the park will get run down or won't be maintained. In fact, if you look at the existing old fields (used to be 1~4, but now 11~14), they are in great shape most of the year. Those fields have been open for several years under the free parking.
So when you say "top facilities", where do you mean? Are you comparing to the Grand Park or Disney/ESPN? I've been to both and the grass is nicer at OCGP. Turf comes and goes depending on the usage but its the replacement cycle that one cares about. I cannot think of any facility in SoCal that's better, when you think of the entire venue.
Last, I am not an Irvine resident or City Council meeting troll. The club my older kid played for at the time, the head of the club's brother is/was the lead lawyer for FP that negotiated the deal. The club had a big to do event for support passing of the phase that we're now enjoying.
Based on this article, it appears the City of Irvine and not the County of Orange is responsible for maintaining the Park: http://www.ocregister.com/2017/08/0...s-park-which-is-twice-the-size-of-disneyland/
Regardless, we have seen this type of project (albeit on a smaller scale) time and time again. So here is what I believe based on experience with developments.
The developer comes in and builds the thing and maintains the park/facility until the developer has built out the last of the homes and vacates. At which time the City/County/HOA takes over. The new party taking over is given this beautiful thing. A year or two passes and the City/County (in this case) looks at its budget and says ... whooaaaa. Why are we aerating and verti-cutting the fields every month? The field manager says "Great question, you see, the developer installed these fields and the lay out of the lights prevents us from moving the fields so we need to aerate the Referee areas, the center, the boxes, etc.; we also need to top dress the fields and sod the heavily damaged areas (boxes and center areas)" The City/County says "Ok, but our budget is $2m for a field crew, equipment, sand, fertilizer, etc." The field manager says ... but, but, but ... I need $2m just for remediation work this year to repair the damage due to use, plus my normal budget of $750k for my 6 person crew, equipment, etc.. The finance guy at the County say ... not my problem, you have $2m, make it work.
Before you know it ... the fields are looking a little neglected. Fields get shut down to rest, because the City/County budget doesn't allocate enough.
I'm not trying to be a Debbie Downer here, just pointing out that in the State of California, there isn't a single County/City park project that is able to maintain quality fields. The Great Park is a great thing, and fills a need in OC, but the pessimist in me doesn't think it will sustain itself once the City steps in to maintain.
With regard to your other question, when I refer to top facilities, I'm referring to the privately run facilities (Silverlakes, Polo Fields, and Galway Downs). None of these appear to have the total amenities as Great Park, but all of these facilities will likely put 2x more money into maintaining field quality than a City/County run park. That said, its speculation on my part ... time will tell.