Again, fair points.
In terms of signing players to long-term deals: we have Kane, Sanchez, Son, Lamela signed, i believe.
However, Eriksen and Alli are not signed to longer deals as far as i know; Eriksen in particular is possibly our most important after Kane and unless I've missed the news, him not signing like the others mentioned above is quite a big issue when we haven't made signings, i'm sure he goes into next summer with only 1 year left which is not a strong position to be in at all imo.
I very much take your point of squad fillers and i do wonder how much they are holding us back (the inability to shift them) but that being the case we are suffering from:
A) Pochettino buying a few too many players who in the end are not good enough and we are taking a hit in terms of struggling to shift them; or
B) Levy far too often goes for the 'cheap and cheerful' option and asks Pochettino to make do and now we have reached saturation point and even Pochettino has said "No more"
I also wonder how much we are overestimating our squad as well...we stumbled over the top 4 line in the end last season and we really shouldn't and it's quite feasible that the squad as it is has only got so much more to give (two of the key CBs reaching an age where we might not be able to rely upon them as much, Dembele and Wanyama likely at their physical limits, a possible hole at LB etc)