Greetings,
MarkovichNimzowitsch would have turned in his grave to see the d-pawn allowed to advance like that!
Certainly she knew what she was doing - the times on the clock clearly indicate that (1:27 - 0:17 (!!)).
Udav18As others have picked up, I think you are talking about "sound" when you mistakenly(!?) say "solid".
One might say that, of the two, the Semi-Tarrasch is more "solid" provided the centre doesn't fall into White's hands. Both, certainly, are "sound" against equal or lesser opposition. Against World Champions,
any opening would be made to look/feel unsound!
As with any opening, it depends on who knows and understands more about the underlying strategies, the (thematic) tactical traps and possibilities, and so on.
As with any openings with such unbalanced-equilibrium based on piece-play compensation for positional weaknesses - such as the Lasker-Pelikan-Sveshnikov - if you don't manage to use your pieces actively, you'll be left with being tied-down to defending the pawn weakness.
Do you prefer open positions where you can use your pieces in preference to concerning yourself with weak pawn structures? Do you play such positions well? These must be your criteria for taking up this opening - not whether the current top GMs or World Champions are using it. Tournament and club players continue to follow the trends of the masters long after such masters have changed their repertoires. New rising stars have their own favourite openings - not necessarily the ones the rest of us fancy!
As has also been noted, the standard positions can arise from the Reti, Catalan and English openings.
You need to know - and be comfortable with - the IQP.
As you are a ~2100 player, I'd heartily recommend Baburin's book on this (Winning Pawn Structures) - assuming you're not averse to hard work, it will teach you a great deal about this important theme in chess, both as a advantage (as "point" for a attacking springboard) and a disadvantage (how to attack it and tie the opponent down to defending it).
Any earlier books on this theme may well also be of help - Nimzowitsch's opus comes to mind, though certain of its strategic solutions may well be out-of-step, if not out-of-date, with modern thinking on the IQP.
Kindest regards,
Dragan Glas