It is theoretically possible for a collapsed or restricted line to also cause the clutch not to fully engage (or at least not as quickly as you'd like) due to not being able to release the hydraulic backpressure through the blocked line.

You typically see this sort of thing with brakes, which work via the same/similar types of lines. A collapsed brake line can cause the brake caliper to appear "stuck on," causing drag and pad wear, etc., and people may drive themselves nuts replacing the pads and calipers over and over again without suspecting the line. In brakes this is reversed, since applying pressure causes the clamping force to engage rather than disengage.

A worn or otherwise janky throwout bearing is unlikely to cause clutch slip. Worn, broken, or incorrectly installed clutch springs might. Worn clutch friction plates, definitely. Contamination from leaked brake fluid, also sure to cause slippage. There's something else to check.