I keep losing crystals to TF2 (Help)

 
I know, right?!  It's almost as if the new frenetic Steam players are catching-on to the wisdom of the old methodical iOS players.
 
The new version of the Tortoise vs. Hare parable retrofitted into an Asynchronous Race motif. 

A well-executed crystal rush is always difficult to defend, and there are no easy answers. That said, there are a few key points to remember in this specific matchup:
 

• Prioritize assault boost tiles. If you are consistently losing to crystal kills, chances are you are not protecting these tiles well enough. Crystal kills are next to impossible without tile support, so be prepared to KO any unit setting up shop there. This is where TF2's squishiness can really hurt them -- only the Spy and Heavy are any good at holding tiles, and even they go down quickly to upgraded attackers or burst-damage items. Also, you don't always need to stomp when taking out these tile-holders. Force them to use respawns or move their Medics forward -- either way can help you in the long run, especially if it gives you the opportunity to easily take out their healers.
• Be conservative with your own healing. A good crystal rusher will seldom waste AP taking out low-priority units, especially if it could invite counter-attack. Keep your key attackers safe from stomping where possible, but don't feel the need to top off every single unit. An AP wasted on unnecessary healing is one more opportunity for your opponent to deal crystal damage. That said, make sure you DO heal where it IS necessary to avoid easy stomps -- this is where good players know they have to actually do the math.  ;)
• Splash, splash, splash. Use any AOE trick in your arsenal to damage/KO multiple units, even if it doesn't result in an immediate kill. Forcing the crystal-rusher to slow down and heal is crucial to withstanding their attack. This doesn't mean you should use your Inferno or Soul Harvest at the first opportunity, but it does mean you should look for ways to threaten and damage as many units as possible, whenever possible.
• Perform crystal triage. Not all crystals are equally vulnerable. For example, the center crystal on the Tribe map and the large crystal on the Dwarf map are both easily destroyed if enough AP are thrown at them. Don't knock yourself out trying to unnecessarily protect these crystals from harm. Instead, if your enemy seems hell-bent on taking out these crystals, use your AP to get into strong position to counterattack, take out their offense, and protect the remaining crystal(s).
• Be smart with your equipment. Don't load up all your items on individual units until the jarate is gone. Spread defense mods around based on positioning and threats. Using items, defense tiles, and positioning, try to make every single unit at least somewhat resilient and threatening. Your goal in this regard is to pressure the TF2 player into using their jarate on a unit that has NOT been fully upgraded. (Of course, once that second jar has been thrown, go crazy with that uber Void Monk!)
• Choose your targets wisely. For crystal assaults, your primary threats are Demomen, Pyros, Heavies, and Soldiers (probably in that order). Attack appropriately. Snipers SEEM dangerous, but they are actually pretty limited in crystal attacks. Don't ignore their damage, but don't sacrifice units trying to take them out if other, bigger threats are on the board.