It appears that the lint screen may not be catching all the lint that it should.
Lint filters never catch all the lint. You probably have already checker that it is not ripped and that it fits correctly in the holder.

There is a lot of lint ending up in the exhaust hose that builds up over time. What could be the cause?
Depends over what time frame it is building up as to whether is is abnormal.
Possible causes could be
1. A dirty or loose blower wheel, not pushing the air out with enough speed
2. Exterior vent louvers not opening up all the way slowing down the air flow.
3. A vent system with a number of 90 degree turns.
4. A vent system with a long run of corrugated plastic vent tubing which likes to hold lint.
5. A vent system that is under-sized.
6. A vent system that is crushed causing an air flow restriction.

Only thing I can think of that would bypass the lint filter but still get the lint into the venting is a cracked filter housing.

If you have a front load washing machine the clothes will have less lint than a top load.

Not as far as I know.