Well in the late game but especially in the endless mode lvl 50+, when you have all the artifacts and most upgrades, runners do move very fast. But yes their bottleneck then is gathering speed (YEET does help somewhat, though that will still be fixed to throw further) and the general fact that game hasn't yet been balanced for lvl50+ so the many producers vastly excel the one single collector. Bulldozer will definitely help with that, but so will adjusting/adding more runner upgrades, tiers and ways to keep them going. And btw yes ores slow down runners but if you buy Rhino Legs that penalty is reduced, even to 0% at max tier.
Best current way to protect against rocks besides dodge/beardAura and turrets, is laser cannons upgrade that makes them destroy rocks, which can eventually even make rocks too weak. But I'll be adding more ways to protect runners, and in general there is still a lot of tuning to do for all these systems. Was even thinking of an upgradable defense stat that reduces the odds of falling rocks spawning.