While i can understand your position its much easier to simply increase grens to 5 man squads. or at least have an upgrade to do so. the only way to prevent 1 shots as you suggest is reduce every single tanks aoe to 1.5. and then they become crap so you need to decrease tne scatter and then you have tank snipers.
They could also buff tank MGs in compensation, which frankly I'd be entirely happy with for keeping the one-shots down.
Would also require dramatic vet changes though since then infantry vet actually would greatly aid their survivability against tanks, tanks would probably have to get their reload and scatter bonuses compensated with vet causing their MGs being changed into a similar-but-far-more-accurate version (a bit like how Pack Howi used to fire HEAT rounds all the time once they hit vet 2).
Would not fix grenades, though.