Stroke Rate vs Stroke Length, which is more difficult?

This topic may have been discussed in the past but a search gave too many hits. I am very interested by your comment and advices for the following real scenario. This is for kids but may be this could apply to masters. BTW, I am just a parent swimmer, very interested in swimming in general but unfortunately not a good enough swimmer. Two age group swimmers (11-12 years old) coming from different swimming history have opposite swimming style: Swimmer 1 (let's call the higher stroke rate swimmer) swims 50 meters freestyle, taking 60 strokes. Swimmer2 does it in 45 strokes, with a time 0.5 to 1 second slower. In general, Swimmer1 beats Swimmer2 in all distances (freestyle and back). Including a 2000 meter freestyle test set, faster by about 20 seconds. In this particular 2000m, aside the time and stroke rate, Swimmer2 (slower stroke rate) did it with even splits while Swimmer1 positive splits toward the last 25% of the distance. Q1. Assuming two swimmers have similar aerobic conditions, which one will have better margin of progression? More exactly, would it be "easier" for Swimmer1 to improve the technique or for Swimmer2 to improve the Stroke Rate? Q2. What would you recommend to these swimmers to get better? To these two swimmers, stroke rate seems to be the winning bet. Swimmer2 was taught with a focus on excellent technique (and indeed looks better in the water), but is confused as this skill doesn't translate into better performance. Of course, we are talking about SL and SR relative to a context where the swimmers already know about swimming. Thanks you in advance for your help.