Just let your Fighter have Dex as his main stat instead of Str. Add the background you want for the skills/proficiencies and you have a lighly armored Thug stabbing away with his Rapier, adding dex to both AC, to-hit, damage, Dex-saving throw and initiative. He is also very decent with ranged weapons (due to the high dex), perfect for an ambusher.Also HP.
That is the issue. I want ambush warrior.
The rogue is too squishy, especially when you don't go heavy on Dexterity.
The fighter can fight but lacks any features that favor stealth or ambushes.
The 3e UA and the 4e PHB both supported this type of warrior. A warrior who can fight both fair and unfair.
Bugbear style. Batman style. UniSoft Assassin style. You see two guards at the door. You sneak attack one and and melee the other.
Alternatively, make a mountain dwarf rogue that's strength based (still uses the rapier in melee) and put a 14 in dex so he gets a decent AC in his medium armor.
To me it looks much easier in 5e to make a thug-type of character, especially if you want dex as your main stat. Something that to me looks like a very good choice.