I'm a little confused. There's apparently a 30 amp subpanel in the garage(I think?), but the electrician wants to install/upgrade a 40 amp breaker in the main panel. That implies to me you actually have a 40 amp subpanel in the garage now. Its a sad thought, but I'd also be checking what type(gauge) of wire is connecting the subpanel. There's more than zero chance it can already support 50 or 60 amps and the electrician wants to jump to 70 to justify an extra $1500 in work. I'd also probably jump it to 100 if the increase is actually needed.

But even with only a 30 amp subpanel in the garage, you should be able to get 24 amps of continuous charging, which should be plenty for most peoples purposes. What else is on the garage subpanel now? Garage door openers don't count at all.

Even if you go with upgrading the subpanel, once you add the cost of the rainproof enclosure, the WC will be cheaper than all the stuff needed for the outlet(the outlet, GFCI, enclosure, ...)

If we assume for a moment you have a 40 amp subpanel already, unless you have big loads out there, the UMC would get you 32 amps of charging(29 mi/hr). If you put a new heavier wire in to increase the subpanel to 70 amps, you'll still get exactly that 32 amps of charging from the UMC connected to a 14-50 outlet, because that's the max of the UMC. You might be doing all this work to get >MAYBE< 8 more amps of charging(aka ~29 mi/hr instead of 24 amps(~22mi/hr), if we assume you have a 30 amp subpanel, or absolutely ZERO increase if its really a 40 amp panel now.

Unless you have a real need for more charging speed or significant other loads in the garage, I'd just stick with what you have and either install an HPWC(inside or out) or outlet(inside only)