How hot is too hot ?
Two measures of "too hot".
1. Engine temp is so high that it can cause damage. This will probably involve temperatures over 220 degrees. The "HOT" light on the dashboard it typically triggered by a switch that closes at or above 240 degrees. In any event, if the coolant is BOILING, the engine is too hot.
2. If the engine temperature at idle or cruise
is more than ten or fifteen degrees above the thermostat rating, the thermostat has lost control of the coolant temperature. This can be from many root causes; typically a radiator that doesn't have enough heat-rejection capacity; missing cooling-air ductwork, a fan system that's under-sized or defective, or an engine so far out of tune that it's creating excessive heat.
You're looking at #2. Your engine isn't hot enough to cause damage, but the cooling system cannot handle the heat generated, so the temperature climbs well beyond the thermostat rating during ordinary driving.
There are one or more problems; you haven't found it/them yet.
why was the car without one ?
The usual reason for removing the thermostat is that the owner is too lazy to find the REAL cause
of excessive temperature. I guess that happened to you, prior owner yanked the 'stat rather than identifying and fixing the true cause.