4231 with 2 defensive mids (Dier/Wanyama/Dembele) gave us by far our best season in 16/17, albeit a little bit defensive looking.
The rise of Sissoko has been great, but the decline of Wanyama, Dier and loss of Dembele has hurt us and stopped us playing this winning formula.
I like Winks, Eriksen, Dele - but if you put any of them in the 2 man midfield it's simply not the same system.
I don't believe we lack or lost quality in defence or attack since then, Walker wasn't that important. It's the midfield cover, breaking up play in different areas, positions taken with and without the ball, and of course the transition from defence to attack that I identify as what we do differently now.
At the time I remember Dembele blaming the narrow pitch of White Hart Lane causing teams to set up defensively in the middle against us. Whether or not that's the case, we scored more and conceded less then.
The last 3 seasons we conceded 26>36>39 league goals. 0.68 to 1.03 per game.
As for goals scored, 86>74>67. 2.26 to 1.76 per game.
Goal difference, +60>+38>+28
Really concerns me having a 32 goal swing in our goal difference in a 2 year period.
So in regards to transfers - it feels to me like the system, or lack of personnel to implement and repeat a winning formula is more the problem. I don't rate Dier, but believe we missed him more than I would like to admit, or at least the duty he performs. Would maybe say his most useful quality was winning headers all over the midfield. I like the idea of Tielemans, Ndombele and other good footballers we have been linked with - but there's perhaps an argument for getting Dier back fit, and bringing in another central midfielder over 6ft next to him / Sissoko (as Wanyama and Dembele are) rather than these smaller (in frame as well as height) creators?
I think walker (and rose) in the 16/17 season were far more important than you seen to be alluding to. Firstly, they were both playing very well, secondly they were our source of width... and finally, Walker could actually take players on - something tripps is either scared to do or cannot do - so whilst his crossing may not be as good, he could get in behind teams. Just look at the dippers fullbacks, 30 assists between them this season plus goals as well... during that 16/17 season we had the best fullbacks in the country...

