From a pure engineering perspective I absolutely agree. I'm too young to remember the P34 or BT46 in person but the shock of seeing different approaches is definitely sadly missed.
In sporting terms though, I (sadly) think they've gone down the right general path. Partly for containing safety as there's no denying that some of the developments have been less than ideally safe to put it delicately - the idea of the combined evolution of an MP4 ground-effect car with the 1500BHP Honda V6 turbo, but with another 25 years of development, just wouldn't be manageable or safely driveable with the lateral G it could generate. Also though, for cost containment - F1 had spent too long going up expensive blind alleys that served no competition benefit.
This is a benefit of LMP racing though for me, which I love to watch. The diesel cars may sound a bit odd but the sight of a Peugeot 908, Audi R10 and Lola Aston LMP1 thundering through the Becketts-Maggots complex while picking their way through the GTs is just awesomely impressive, and you can continue to see genuine differentiation and innovation in the chassis.