useful for airline screening, but be wary of presenting it to immigration if they ask as they are watching for these unpaid tickets now for people with long recent history in Thailand.
only difference with DTV is people are mostly existing and re-entering to extend their stay each time, so potentially no further checks on their financials unless border security decide to start checking in the future.
in regards to marriage and retirement visas, they go through the checks at foreign embassy’s when people apply for it as they need to supply the required bank statements. Thai immigration do their yearly checks when it’s extension time. So correct, there’s zilch checking at the border for those visa holders.
if you have a history of around your 90 or so days a year in Thailand the immigration officers shouldn’t bother you having a return flight of 87 days as you describe.
the immigration officers will screen you on a case by base basis, taking into account how close you are to being in country for 150 or so days in past 12 months to determine your travel intention. They are screening for illegal workers and potential scammers.