I think that you're both right.It's not, it is because they have had some very good players but are a small club (relatively).
Trust me, if clubs bigger than yourselves really start to come after your players you will lose some. No club is immune to this its just that Southampton are lower down the food chain and have been fortunate/unfortunate enough to have had players good enough to attract teams higher than them.
Spurs are quite high up that chain so only have to worry about a small number of clubs but, as was seen last year with Neymar, no team is safe.
If teams come in with big money and are massive clubs, then virtually everyone will struggle to keep their players.
Southampton have been in a bad position because they've produced good players and can't afford to keep them.
So what can they do? Most of what they're doing is right, but they need to address two things.
The first is the manager, which we basically ****ed them on, though they did some damage there themselves.
Having a coach that the players believe in and think will improve them and and the club is massive.
Shifting out Cortese cost them Pochettino and they also messed up by sacking Puel, in my opinion.
The second is playing hardball with teams that come in for their best players, up to a point.
Selling van Dijk for £75m is good business. Do it when you've got a suitable replacement and there's no problem.
Timing is everything and planning these things out makes a massive difference.
Their impressive academy makes this even easier.

