On the surface it would seem like there has been very little improvement in boards, and perhaps there hasn't been that much major change, although I would have thought there would have been a noticeable difference in the ride between the Gambler and the Jaime SLS.
Weight would have been the first obvious difference, with rocker being a close second. Gamblers were essentially a wakeboard with wake type rocker and heavier construction to cope with the loads of boots.
Modern boards are improved but in more nuanced ways. The type of flex, and where/how they flex. It has become a finer art of making the board twist and flex in a way that delivers more crisp pop or better holding or better dealing with choppy water, depending on the style you want to ride.
But yes, there is little change to a generic board in the last 10 years or more. The biggest change in board design was moving away from the foam core designs which would break. Since paulownia cored boards hit the market, the boards flexed better and were more resistant to breaking. 3D shaping of the deck allowed more controlled flex.
Modern high end boards are definitely better than older boards providing you have the skills to exploit the characteristics of the individual board. Meaning, if you are just riding in and out, you can ride anything and they all feel similar with exception to how they handle choppy waters. However, an experienced rider will notice the difference in terms of pop and subtleties in the ride when riding at a higher level.
The bad thing about modern boards is the price is getting well up there, with some decks being as much as $2000 or more, plus footstraps!

. The counterpoint to this is the boards will likely last you a lifetime, so long as you replace worn out footstraps every few years, and you take good care of it of course.
DM