Aeon is a speculative investment since 99.9% of anyone who owns the coin are not spending it, only holding or trading.
Bitcoin is being used, integrated, and speculatively held on a daily basis. Bitcoin will also be around in its usable state until supply is exhausted, someone breaks sha256, or finds a severe security flaw that rendered the chain useless.
Most crypto coins with a tail emission could, and probably will, become obsolete soon after tail emissions kicks in and miners realize there is close to zero incentive to continue supporting the chain and it eventually dies off well before bitcoin can. The only way any cryptocurrency on tail emissions could survive was if the value increased exponentially to create financial incentives to continue mining operations. One of the reasons a specific project made an incredibly gigantic supply so it could literally never run out of supply in the developers lifetime.
The argument was not how the coins mentioned are presently used but on their monetary policies and how they might affect on how they could be used in the future.
Grin's monetary supply dilutes the coins of early adopters and disincentivizes them from hoarding. I reckon Aeon's tail emmission might help stabilize the price assuming it was adopted a certain % of bitcoin's adoption. Bitcoin's monetary policy of fixed supply will tie it forever as a speculative asset similar to stocks.