You definitely cannot leave and immediately reenter for another 3 months.
You must leave for 3 months before returning. It’s 6 months in any one year.
Thailand are merely attempting to enforce their equivalent policy.
Can you imagine if the Cheap Charlie’s a la Thailand attempted this: all the groups would be full of “…how can I rent an inflatable dingy to go to Dover for a day then return that evening”?
The rules changed in tourists’ favour ie longer period of 45 days for visa exempt. And that’s extendable by 30 days.
That some over stay or continuously attempt visa bounces is a different matter as and - as always - subject to the immigration vagaries but at least there is some form of latitude. (The rule is stated regarding the number of land or air entries permitted per year too)
Maybe if we compare this to what would happen if one tried the multi-visa-bounce-cheap-charlie plan in europe, usa or better still, The Middle East. Rubber glove time.