I can't speak for the USA but in the UK our radars do not show weather so ATC can be of little help in offering avoiding action. It sometimes comes down to an aircraft which has gone through some weather reporting how bad it was and then following aircraft making decisions based on that information. Of course, weather radar on the aircraft plays a huge part - but it's not always right!
On countless occasions as a Heathrow Radar Controller I have experienced severe weather which some crews would fly through and others wouldn't look at it. The only advice ATC can offer in extreme circumstances are weather reports for possible diversion airfields...... or maybe route a/c to holding areas known to be clear of weather. At no time will UK ATC direct an a/c to an alternate because of bad weather at the destination - it's wholly up to the crews, as it should be.