You have made quite an austute observation , and accurately so of both engines, keeping in mind that I favor Jensens & am currently into Wilesco's , I would choose the Wilesco D20 over the Jensen #75 for most of the reasons you discussed . I differ with you a little bit in that I think the Wilesco fire box is better looking , Jensen refuses to use heat resistant paint & thus they look bruised very early on. if you take care of a Wilesco boiler (empty it and keep dry when not in use) , it will last a long time . both throttles have their own special quirks , a Jensen throttle tends to leak and are not very good for incremental adjustments (an important benefit) Wilesco throttles (the wheel type) don't generally leak but are finicky to use ,many times I've went to turn it in and have the engine speed up first before slowing down , if you pull up on them as the engine is running the engine Will speed up, it has a rubber bushing that is a little spongy until some steam passes through & the threads don't appear to be all that precise. The standard Wilesco stanchions (bearing towers) are better than the Jensen stamped tabs on the #75/25 , but the Jensen are more than adequate and I've rarely see one worn oval. I also believe the Wilesco faux governor is superior to the Jensen, the Jensen governor robs a noticeable amount of power and therefore I usually don't connect the spring on my Jensen (when not making a video) not so on my Wilesco's. The bobbing of the Jensen reverser is proper and needs to occur , any attempt to circumvent this activity will result in the valve not opening or closing unrestricted and will cause poor running....or no running at all. The connecting rods on both are adequate for they're specific applications.(Jensens #75/25 have a replaceable connecting rod pin/screw) Now if we were comparing a Jensen #20 to a Wilesco D20...hands down the Jensen #20, leagues apart !
My 2 1/2 cents worth. (I do currently own all of these engine plants)