Yes they did discontinue the 18XX Thunder series, kept the 14XX Performer series and a added the AVS 19XX (annular discharge primaries) series.
I don't think the discontinuation has anything to do with the kit you need. Edelbrock was in the process of switching their US foundries locations in early 2020 and have had a tough time getting back up and running.
I am a fan of the AVS2 vs the Thunder. I had a 750 Thunder and it always felt a bit sluggish at the off-idle tip-in. Switched to a 800 AVS2 and it works great. Very responsive. I did do some AFR (remote wideband) jetting and metering rod tuning but it only took about 2 hours to iron is out.
I'm in the process of going dual quad and ordered two 1904 AVS2 today.
Something new from Edelbrock for the Holley fans is the VRS-4150
https://www.edelbrock.com/vrs-4150-carburetors