I feel the same way about Tailspire as I feel about pretty much every other VTT. They might do okay, even pretty well, at combat maps and/or character sheets, but I want is
the whole game world in the computer. Maps are just a fraction of what I need as a GM. I need data on economics and population numbers and power structures. And I need computation over all those things.
For instance, my game rules include an economic subsystem, which takes in the production of goods and services at hundreds of in-game cities, and computes prices for over a thousand player-purchaseable goods. The "second app" that I referred to above allows players to (among many other things) purchase stuff at the market nearest their current location and have those items go straight into their character sheet. If the "item" is actually an animal, a hired mercenary, etc. then a different subsystem generates a new NPC with the right statistics and attaches the player to it as owner/liege.
I could write an extension for a VTT that talks to my economic system over an API, and throws items up on screen, lets players purchase them, moves them into their character sheet using the right function calls in the VTT's extension library, etc. But every step of the way, I would be fighting to cram this subsystem into the VTT's conception that gameplay begins and ends with maps and char sheets.