I figure we've got a few things going on, as we age. Load-bearing strength exercising doesn't have good alternatives, and it can impact strength, bone density, muscle mass, and BP/cardio. "Cardio" activities don't really have good alternatives, either, being generally the better options for keeping the heart stronger, blood vessels prevalent (ie, in extremities, where flow reduction can cause all sorts of problems), BP in line, etc. Makes sense to mix a range of exercises, to keep all "cylinders firing" properly. Even if the level of performance keeps going down as we enter legit Old Fart status.

I'm with you, though. Adding a moderate amount of various other activities can have serious benefits. Yes, if there's only time enough to devote to exercise, then doing different things will "take from" the time allocation. But then, you get those benefits as well. You can, though, alter the type of cycling you do, or the type of rowing, etc. Long/slow distance is one thing, and in many ways provides (over the long-term) cardio in a way that isn't easy to achieve with other methods. But you can alter cardio to incorporate much interval-based training, hill-based training, etc. Can provide cardio but strength as well, while doing the "cardio" activity. Likewise, strength training can be just sitting doing dumbbell and barbell exercises. But, one can also do circuits and choose a greater number of exercises that are compound (multi-muscle-group) motions, yielding vastly greater cardio and muscle involvement for the given amount of time. Lots of ways to slice that onion, IOW.

From back in my running days: started doing mostly mid- to long-distance runs at moderate pace. Got much fitter. But then began to incorporate hills and/or intervals/Fartlek speed work into the training, along with varying the distance and challenge of the routes selected as the week progressed. Vastly more challenging, got me stronger, was tougher cardio-wise (though for shorter periods), allowed in-line recovery stints despite the harder work, etc. Became a much, much better runner, mostly through variation of the training in such ways. Better cardio, much better strength, better flexibility, better ability to withstand "curve balls" thrown at me on an unknown run. Could be applied to running, rowing, floor/strength exercising, etc.