That would be a mistake IMO.
Although the game appears to have a rock-paper-scissors system to fighting the reality is that Range>Everything in combat here.
I have operated along these lines and can recommend a hierarchy (Elves).
For everyone the mainstay of offense is the LR, Archers and, later, Rangers for Elves. Because of this I upgraded Needles up to lvl 12 quickly early on.
Then I began to realize how often an Elf uses Golems. They seem to be present much more than LR. Being both capable offense and even better defense they enter battles both with and without LR. Therefore, although my Dr Abbey (Mage) had been sited, I upgraded ToT until it reached 20 or so.
Along the lines of troop frequency, the Monastery (Sanctuary for Humans) takes top honors. While I was upgrading the above, I was also upgrading my Monastery sporadically because it benefitted
every troop on the field. Finally, when I had LR and HR reasonably buffed (lvl teens to twenty), I made the commitment to max my MM first. It is a particularly KP costly AW but, to repeat, it benefits every troop on the field.
Mages are great and I love using them but my MF strategy relied on them much less than LR and HR. Therefore, based on frequency of use, I maxed ToT next.
After bring Dr Abbey up a little more to keep up with the tougher fights, I chose to max Needles.
Finally I just finished maxxing DrAbbey.
Needles to say (pun), I concentrated on troop
strength. Now I am leveling up training queues (already sited but researched usually only while my main AWs were upgrading).