At the start of the war, the french had the most powerful tanks in europe. the above mentioned Char and Somua.
on paper that is.
The somua was for its time a true work of art. it had excellent suspension and transmission, a rather good gun (for the time) and heavy armor for a so called 'medium' tank. Its biggest drawback (which all french tanks had) was the poor visibility the tank cmdr. This was the leading cause of the somua's dying to much lighter tanks that managed to flank and blast them.
The char... well the char was a nightmare. it had extremely thick armor, a huge gun (for its time) and, like the somua, had very poor visibility for the tank cmdr. In fact, the tank cmdr was a miserable person in that tank. Not only was he supposed to lead the tank but also load, aim and fire the top turret cannon all by himself. The germans noticed that they could catch the char by surprise very easily after its infantry support had left (or killed) .. the poor cmdr inside was too busy loading, firing the gun and telling the driver where to go to have time to scan around to see if anyone was flanking them. and thats how they were killed off by AT infantry and lighter tanks.
Both of the above tanks were designed as INFANTRY support tanks hence both were very slow so the infantry could keep up. fighting another tank they assumed would happen on a head-on scenario or the tank was to fight off artillery pieces on the enemy's defense line, that is why these tanks had heavy armor up front and yes, it was sloped armor (more of a curved down slope really).
but.. the french tanks were completely outclassed by the panzer 3H and p4 versions that appeared shortly after france fell. The germans used their tincan little tanks like the pz2's, Pz1's and the pt38 (all had peashooter guns and armor that was merely infantry bulletproof for all purposes.. a .50 cal would slice through them) that were insanely faster to bypass , encircle and let the artillery and air kill off the heavy french tanks.
Your friend is dead wrong unless he claiming France had the best tanks in the first week of the war.