Do new consumer routers still "need" aftermarket firmware?

I don't think you realize how powerful OpenWRT is. It's a whole Linux environment where you can write your own shell scripts and schedule jobs, etc. If you have created a set of your own personal customizations over the years, then it is nice that you can bring them over onto any subsequent OpenWRT-capable router you buy.

Yes. Bought a recent Linksys to replace an extender, which was running OpenWRT. The new Linksys doesn't support OpenWRT (bought it in a hurry), and apparently Linksys doesn't support SMB[0] if the device is extending another network, which is BS since we were able to with the OpenWRT device.

[0] https://www.reddit.com/r/LinksysOfficial/comments/142mnnr/er...

How much do you trust them to get it right and do security patches? There's a chance D-Link's problems are common across vendors, and they're ones being honest about it.

That's a very subjective question. What do you want your router to do, and can it do that out of the box?

Two reasons

1. Updates, every single router manufacturer abandons their routers within a few years, so you either keep buying new ones when the updates stop or you use open source firmware that extends that life until it's obsolete.

2. OpenWRT (and the others) expose all the features you need where manufacturers often simplify this or charge you extra for them. The hardware becomes use to utilise as you please.

I wish Netgear and others directly supported open source firmware like they did in the past.

You mean firmware for all the proprietary hardware they are full of like Wifi? Likely yes.