Date of click is fine as long as you are understanding your reporting over fixed timeframes. e.g. What is my Day 7 ROAS on spend from 2 weeks ago, that will never change once you get past 7 days from the window of spend that you are looking at.
Date-of-conversion has the different (and in my opinion worse) issue of being 100% accurate in terms of current cost-per-conversion but under-values all marketing channels. This is because it attributes the cost of visits only to conversions that have already happened, while more conversions may later be attributed to those visits. This means that a conversion based model is actually worse for channel analysis.
Agreed on both points. Ultimately, everyone should try to gain a better understanding of the duration and number of touch points in their sales cycle. This directly impacts the lookback window you set. It is also important to know what these are when comparing any data across platforms.
For example, right now I'm going from a 90 day window for certain goals in AdWords because I know that while the majority convert on that goal in ~30 days, there's a long tail. Unfortunately, Marin restricts their window to 30 days, so any deeper digging will need to occur within Google Analytics or data from our data warehouse.
Would be great to learn more about solutions you've seen in the wild since it seems like you have a lot of experience on this topic. If you have time for a chat my email is in my profile (tried to find you but shostack is ambiguous :)
Date-of-conversion has the different (and in my opinion worse) issue of being 100% accurate in terms of current cost-per-conversion but under-values all marketing channels. This is because it attributes the cost of visits only to conversions that have already happened, while more conversions may later be attributed to those visits. This means that a conversion based model is actually worse for channel analysis.