For the past 20+ years I've been working on a laminated MDF TS extension wing that holds a router lift. There have been times wood has caught on the edge of the router plate. Wood swelling? I don't know. But it's annoying, and if it snags part way into the feed, it can mess up the job.
I recently bought a new cabinet saw that has cast iron wings plus a phenolic extension that looks insufficient to hold a router lift w/router motor over time. The phenolic top is 3/8" thick. The frame is 5/8" x 1-5/8" phenolic. In order to install the router lift, the center rib has to be cut, leaving a span of almost 20" unsupported. Of course I could beef it up but it would probably be easier to just build a new extension wing. I could use that extension on the TS outfeed.
The TS manufacturer sells a pricey cast iron wing that fits the TS and router lift perfectly. About the only drawback I can think of (besides price) is rust.
Phenolic sheet goods, from what little searches I've done, look to be considerably more expensive than laminated MDF. I know nothing about phenolic but I wonder about it sagging over time. I bought some 3/4" thick UHMW a couple decades ago, thinking it was completely stable, but over time it proved not to be.
As to MDF, from my experience, laminated MDF seems to have its drawbacks, too, as noted above.
Hopefully, the cabinet saw upgrade will make work much more enjoyable. I'd like to have a similar experience with the router table, too. Any thoughts?