I have both the peloton 97 and macpac nitro which is alpha 90.
The peloton in medium is 5oz on the dot. Nitro is about 5.6oz.
The nitro is much warmer than the peloton assuming no wind or wearing a wind shell. This jives with Stephen’s articles, which find that fleece warmth is directly proportional go loft. The alpha 90 had 2-3x more loft than the P97. The P97 fabric is probably like 1-1.5mm thick while the Alpha 90 is closer to 3-4mm.
Both the P97 and Nitro make a comfortable base or mid layer. Most often though, I end up using the P97 as a cold weather base layer or sleep shirt, while the Nitro is better suited as an active mid layer.
The nitro does better as a mid layer because Alpha vents much more effectively and thus opening up a wind shell can remove nearly all Alphas insulation. The P97s woven fabric is better at blocking wind and thus cannot be vented as effectively.
The durability of the P97 seems pretty good. I have not snagged or torn it or had issues with stickers getting stuck in it. Without doubt it is less prone to snag or attract stickers.
Overall I don’t think P97 is a direct replacement for Alpha. They are similar and I like both. Alpha excels at venting and stop and go activity. P97 is better as a base layer, more durable, less prone to damage, but also thinner and less warm