I'll play devils advocate so this doesn't become a one-sided FRA train at the very least.
We should keep in mind that he doesn't attack with just tentacle like jabs. He has hundreds of meters of range and could cover massive parts of a large building with the sheer amount of microbots he had. He can create barriers around him instead or hit him with a large wave that would be very hard to evade compared to just a tendril jab or something akin to that.
Not sure how effective that'd be. He can easily catch said cars with the sheer amount of microbots he has and then he can retaliate by throwing the cars back or even as protection.
That's fair, though I think if Yokai becomes aware of him having a weapon he is very likely to just play it super defensive and create large barriers and attack with walls of microbots he can't shoot through. In addition, Microbots would very likely be able to
1. Take the gun from Wesker
2. Disable the gun by getting inside it and breaking apart its components, blocking the trigger, etc (They were able to tear robots apart and stuff)
That's fair, with his level of regen, the only feasible way to kill him would be to rip him to pieces with the Microbots, or rather opt for knocking him out or incapacitating him instead.
That's about all I've gotta say.