Theres some truth to what your saying,back when syn oil was first coming out people where having trouble becauses the valve guides where made to accept leaded gas,so they where softer then they are to day,and the oil was so full of ditergents it was wearing the valve guides so much in such little time that the cars where smoking badly by the time for another oil change.It is not true to day,the modern cars run on unleaded and last longer then ever before(at least they should...)
But if the engine is a higher milage engine that was never care for then yeah,changing to syn oil mayproduce oil burn off and leaking gaskets,only because the leaks where already there and over time sludge(and carbon) had built up around them,inefect blocking the leak.If its a old engine,or higher miles on it and never had syn oil in it I wouldnt change over from conventail,since the cars been run just fine on dino bones for a long time,and it has provided fine protection.
Now if you buy a old car or truck and have the engine rebuilt(or rebuilt yourself) then it would be great to run syn oil right off the bat,(after break in on proper grade oil)
Syn oil provides less burn off,so if your thinking about going to dino bone oil since your engine that was run its entire life on syn oil,dont,since the oil will burn more rapidly then with syn oil...The only true fix for a smoking engine is a rebuild,But going to a thicker grade(5w-30vs15w-40) oil will produce less burn(plus boost compression a bit in case of worn rings) off then a standerd economy oil...
But this has its own draw backs,more cylinder wear and the canch of spining a bearing if you just hope in and take off in cold weather...Not to mention that it is a little more diffrentcault to start in cold weather.