Nah, you are not downloading from SteamDB, you are downloading from Steam servers, using Steam client, which means you need to be logged to Steam account.
You want somehow for TMP to manage your Steam downloads, whichis I don't think is possible.
Then why TMP peaks 2k players lower in the past 10 days? The number will be back but not before TMP updates.
Some people simly choose to wait because they want to play new version of the game, they want to be able to use newly released DLCs which are incompatible with old version, they want to use mods in the meantime, which, surprisingly, get updated too - all the mods except Promods (for ATS already released) which required update were updated withing 4-5 days, they want to participate in WoT events and WoT contracts, which are also incompatible with old version.
You essentially keep all those people out if you do not update in a timely manner. That should be priority, I don't know which extensive feature and big mods you are talking about, appart from Promods, which will aslo be updated as soon as possible.