Fluorite that is used by the top makers is not leading to issues in telescopes or camera lenses, so you should not make that leading in your consideration. It has proven to be a fantastic lens element in refractors, doing their performance well.
That said, there are many superb lenses made without fluorite, using other good designs and lens materials. In fact, the best corrected 5-6" current lenses are arguably the TOA series by Tak, using two FPL53 elements.
As for the Tak TOA150 vs TEC140FL. Both are superb scopes, with the TOA150 a proven performer and the FL140 likely becoming a proven performer.
The performance edge will probably go to the Tak TOA150, being known to be superb and having a 10mm aperture advantage. The cooling advantage will go to the oil spaced TEC. In an observatory, I would choose the Tak TOA150, because that where it's strong points shine and it's hefty weight and longer cooling time are not so much an issue.
In the end, both should be excellent and vary satisfying scopes to use and own. Best answer to your question would be to side-side them both.
Just my 2 cents.