Quote: "But doesnt that hot air rise (aka thermal) causing lift?"

Since heat causes air to expand, it becomes less dense as it occupies a larger volume and therefore it tends to rise. However, hot air tends to rise unevenly. Often the hot air rises in circulating columns (thermals). This is great for buzzards and sailplanes. But when you are coming in for a landing and "flair", some other factors come into play. When you "flair", your plane will be in a nosehigh attitude, the wing angle-of-attack is increased, total airdrag is increased, and airspeed decreases. Here is where the layer of hotter, less dense, air can ruin your anticipated (hoped-for) smooth landing. A sudden decrease in air density results in a sudden loss of lift, and the rate-of-decent suddenly increases. At this point, let's hope you have a good strong landing gear and plenty of prop clearance.
Regards
JC