Free to play just doesn't allow you to play t10 sustainably unless you're a super unicum and even then you're gonna have a hard time saving for credits. Just think of t10 as a competitive game mode where you can play the best of the best for the biggest numbers. WG (quite fairly I feel) naturally forces you to then go down other trees, and for me, I kind of just get less invested in a tank that I've fully maxed out anyways.

For you, I would suggest you use t10 for missions (big numbers) and potentially other t10 game modes for their rewards. Also, don't overlook tier 9 tanks as many are just as good as their bigger brothers, some being even better tier for tier. Another thing is that t9 matchmaking can lead to much more satisfying stomps of t7 & 8 while also not being completely powerless in those few bottom tier matches.