You are quite right potentially after some reading around on construct performance tips and advice for construct 2,3 and elsewhere.
I've noticed that the best performance comes from trying to keep everything into one spritesheet as possible and keeping everything into one tilemap as much as possible to create interesting environments,etc
The loading time is superb if that is done correctly.
In the end the hardware targets are the bottleneck not the spritesheet size as such it's still best to keep in mind the lower res it is the more faster it will potentially be because of less pixel to load perhaps anyways.
So basically you can create whatever you want within those hardware limitations 2048x2048 for mobile or desktop sprite sheet size though I'm not entirely sure how big one sprite sheet can be before it delays the load however just aslong as you can work with minimal amount of spritesheets and tilemaps at a fair spritesheet size it will be possible.
I think that's the end game so far Id say construct 3 might be better then an snes or gba in terms of performance capabilities with this technique used properly and correctly we might be talking later (2000) pc power here.