For surface use, particularly off-road, features like closed and screw-secured endbells are desired. Integrated heatsinks are a nice-to-have as well. When those features aren't present you're wise to implement some workarounds like taping or otherwise covering up the holes, CA glue or clamping to secure pressed-on endbells, and snap-on heatsinks. A lot of the higher-end brushless hobby-grade motors available were developed for aircraft, so features we may want for surface use were not needed or would even be detrimental for aircraft…open endbell motors in aircraft can take advantage of the cooling provided by the airstream withoug having as much concern over debris fodding-out the motors. Also aircraft aren't typically subject to the kind of regular pounding and abuse a surface vehicle would see which would cause a pressed-on endbell to become dislodged.
I would still rather have a higher quality motor and implement the workarounds than a cheaper closed motor though. It is just nice to see motors becoming available now that are designed from the ground up with surface use in mind. Hopefully some of these motors are also adding larger, more durable bearings. I've heard some folks mentioned that is a feature they would like to see as well once again because of the pounding a big heavy motor with a big 5mm shaft will take during use off-road...would want a big strong bearing that can handle the load caused by jarring those big heavy motor internals around.
I would say, YES! Here is the inside of my Neu 1512 (with cooling holes).
Front bearing before cleaning on left, rear bearing after cleaning on right.
If you look down inside, you can see all the dirt stuck to the front bearing.
Is that dirt in your motor with or without you covering the holes with electrical tape etc? The reason why I ask is because I have a standard Nue 1512 and I electrical tape both ends. If dirt will still be getting through, I may have to clean out my motor more often.