> Compared to gmail accessed via web, email clients offer slower startup
Why would you ever close your e-mail client other than to start the latest version with that security bug fix?
> higher bug count
TB is missing newer features like calendaring (lightning is pretty broken) I'll give you, but they haven't bugged it out with new features in years. If nothing else, TB is at least stable and mostly bugfree for the stuff it does support.
> inferior search tools
TB search worked great before we switched to Gmail as our e-mail provide. Now it's uselessly slow. But with our local e-mail server it was wonderful. Not better than Gmail search, but close to as good.
> a crazily confusing configuration burden
The only thing I can imagine you're referring to is the ability to configure multiple e-mail accounts or something. That's a feature. You can connect to whatever standards-compliant backend(s) you choose. And even some that aren't as standard's compliant as the claim to be (*cough* exchange *cough* gmail).
> create a deep disincentive to access email from any machine but your own
You mean "naturally directs users to work on personal and potentially sensitive stuff from a trusted environment instead of putting their password in to whatever keylogger-infested, malware-toting filthy keyboard and screen they happen to walk past."
> a centrifugal bumble-puppy model for where your emails reside that can be relied upon to place the emails "on the wrong machine" (or none at all, or N-fold on each of M machines) when you need it most, and they bifurcate your message store when you change jobs or ISPs, etc.
Wait...what!?!. Maybe you're still using POP and have some silly config or something, but e-mails are stored on the provider's server. We cache them on the client for speed and offline access here in 2016. Oh yea, we also cache them on the client so when you forget to make a copy before telling the man "I Quit!", you still have them all. Try doing that with Gmail.
> Moreover, I am spared the horrors of the aged hacks and platform-bound kludgery intended to address the above faults
I'll give you the "aged hacks and platform-bound kludgery", but unless you're one of the few brave souls who dares to look at the source code, I can't imagine what of those horrors you actually experience. TB works. It just doesn't do newfangled stuff like google's keyword (to:, in:) searching and calendaring.