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Adventurer
By that logic, finding a +1 sword in a 1st or 2nd level dungeon would "break the math". If giving a character +3 to his stat breaks the early game, the math isn't as robust as the designers claimed.
A +1 in 5e is close to the equivalent of a +3 in previous editions. An 18 ability score versus a 17 is giving a +1 in saving throws, all ability score checks on top of attack rolls or damage.
At what point did they claim it was robust? They claimed the math was tighter and it is. That means each +1 is significantly more valuable than it ever has been and a DM needs to be careful when handing out bonuses.