Great creativity. Everyone at the table can learn from that. I'm not understanding how that is a problem.
Well obviously it's not a problem for you!
But if someone thinks that the PC's skill at being sneaky should correlate to some representation of that skill on their PC sheet (say, their DEX (Stealth) bonus) then there will be a problem for them.
As I've posted already, with quotes from the 5e Basic PDF, there is textual support in the 5e rules for the second person's thought as much as there is for your approach. I think the tension in the text is not only obvious but deliberate - the resolution of the tension by different groups in different ways enables the text to support a wider range of RPGing approaches than it otherwise might. Which is an obvious commercial goal for WotC.
That's why we don't make people give speeches. If a player wants to describe something in first person because that's going to be fun, great. If a player wants to just give a short 3rd person description of how they gave a speech, that works, too. Both achieve the same thing: describing what the character is doing. Both will be adjudicated the same way. There are no in-game bonus points for being a real life linguist.
Why use the word
make? The issue is
do you permit them to do so? At my table, if someone wants to speak as their PC, and it is a powerful thing that they say or do, that is part of the fiction that is relevant to adjudication.
And why are there in game bonus points for knowing about tank traps, but not for knowing the collected works of Shakespeare and/or Churchill? I'm not trying to "gotcha" you here, just pointing out that the line you seem to see as obvious is not self-evident at all, but is a line that you have constructed.
Just as you think
I build tank traps like <goes on to describe the tank traps in general terms, and how they can be build using rope and timber> is a better action declaration than simply
I erect fortifications to defend the homestead, so I think that a powerful oration is a better action declaration than simply
I orate powerfully, pointing out the many sacrifices that have already been made in pursuit of the cause.
That still leaves open how the better action declaration feeds into resolution. There are different ways of doing that; I've posted how I handled it in 4e. I don't think it's as straightforward in 5e.
Bottom line is that we all come to the game with different real life strengths and weaknesses. Creative ideas will vary from person to person based at least partially on their prior life experience and prior gaming experience. When someone comes up with a creative idea that helps the group, that should be celebrated. Seeing those things as something that amounts to "gaining an unfair advantage" is a... strange way to look at it in a cooperative game.
I just think this varies from RPG to RPG. And can vary even within the confines of 5e D&D.
I mean, suppose my 18 INT wizard PC is playing a chess game against the 8 INT barbarian PC to determine <some wacky but high stakes thing that has come to pass in the campaign>. There are any number of ways to resolve this, from straight
the 18 INT beats the 8 INT to
make opposed INT checks to
OK, you two players play a chess game here-and-now. And of course other possibilities too.
I don't think any of these ways is self-evidently correct, even within the confines of 5e D&D. But I can easily see individual 5e players having a pretty strong preference that it should be done
this way rather than
this other way.