assume a larger diameter two blade propeller rotating slowly giving tip speed of 200 knots and a certain blade area, now assume a smaller diameter 4 blade propeller with the same blade area as the two blade prop. The smaller prop has a higher RPM to achieve 200 knots tip speed.
Imagine all else equal, the 2-blade and the 4-blade would have the same angular velocity (RPM) to produce the same tip speed velocity. The velocity of the tips is not dependent on the number of blades, rather on the angular velocity developed from the rotational axis - the centre of rotation.
If you lengthen the blades on one (does not matter which) and do not increase centre speed, the angular velocity of the tips increases and you would have to speed up the centre of the shorter one to achieve the same speed tip velocity.
Example (all numbers are for illustration purposes only):
Two all else equal fans rotating. Diametre 100 cm. One is a 2-blade and one is a 4-blade. To achieve same tip velocity you let both rotate at 100 RPM.
Now you change fan blade length on one. Different diametres, one is 100 cm, next one is 200 cm. All else equal. If you keep both rotating at 100 RPM then the velocity at diametre 100 cm is the same. Velocity
at tips for the 200 cm diametre fan is larger.
The larger tip velocity for the longer blades is because the magic of angular velocity that messes up ordinary thinking. While they have the same speed at 100cm, the longer blade tip has to travel a longer way to "keep up with" 100 RPM and thus it has a greater speed.
This thought experiment is of course performed in vacuum-like circumstances. No consideration to drag or other real world performance issues at all.