Fringe doesn't mean false. There's no problem being a fringe scientist in academia.

The problem is that his arguments are lacking.

His main argument basically is:

1. There is erosion

2. It was caused by rainwater surface runoff

3. It didn't rain much since the last pluvial period.

4. Other monuments have less erosion

5. Therefore the Sphinx is older.

Now, that is a perfectly reasonable argument, but it omits important things. Let's complete it:

1. There is erosion

2. It was caused by rainwater surface runoff (let's grant that, even though much older runoff erosion should be soften/crossed by wind erosion)

3. Climate was dry, but short downpours were frequent, because of aridification.

4. Other monuments have less erosion, because they don't lie in a rainwater catchment like the Sphinx.

5. Therefore ?

Now for the mainsteam argumentation:

1. The sphinx temple was built from blocks cut out from around the Sphinx, so it is the same age.

2. The sphinx temple stands on the perimeter wall of Khafre's valley temple, therefore it postdates it.

3. Luminescence dating of the Sphinx temple produced Old and New Kingdom dates.

4. The Sphinx enclosure and temple were not finished in the Old Kingdom, therefore no cult was established at the time.

5. Hence no old kingdom references exist to the Sphinx.

6. Erosion was caused by heavy rainfalls at the end of the Old Kingdom, wind and salt erosion, additionally the plateau was heavily eroded prior to the Sphinx being cut.