Can I re-enter Thailand on a TR Visa after leaving the country for a short period?

Time to close Stating rules is indeed not enough. The Visa Exempt Entry and the Tourist Visa are desinged for tourists, people who have a break from their jobs and come to see Thailand for a short period of time. But I understand that longer breaks are possible in modern times and you can be a tourist for many years, but for those people different types of visa are designed and believe it or not, Immigration officers are not stationed to carry suit cases. Look on Youtube for multiple series about Immigration in several countries, they all do the same job. Get the correct visa for your puspose and length of stay and the rules are applied, play games to avoid the correct visa and understand the game can be lost.

It also does seem to make a difference if there is time spent out of the country in between tourist visas or visa exemptions. Visa runs, as you mentioned, where you jump a border, get a visa, and come straight back, or a border run with an exemption, is a good way to attract the wrong kind of attention.

BUT Immigration Officers do have a job description and suppose to ask people questions if they suspect abuse of visa rules.

There is no limit on how many tourist visa a person can use in 1 year or any other set time. There is also no limit on how many Visa Exempt Entries a person can use IF coming in by air, if using land borders than it is 2 Visa Exempt Entrys a calendar year.