Quotes from Igrot Ramchal 19
Let us not forget that this is the same Ramchal that wrote Miselas Yesharim

-He satisfies his lofty soul only with the grass of the field, which is the Pshat level of Torah. He makes his life bitter with Kal Vechomer and Gezarah Shavah, on which it is written "they made their life miserable with hard work".

-Is this, [learning only Pshat] good in the eyes of G-D?

-What pleasure does G-D have in all the big calculations and many conclusions, while there is not one person who strengthens himself to stand in the mysteries of G-D and to reveal the light of his Glory.

-Who ever has a sharp mind should analyze at the most for only an hour or two in Halacha. Whoever is not sharp should not study it at all, rather he should spend his time with Midrashim and Kabbalah, the inside of the Torah.

-Why would one leave the main learning [Kabbalah] and go to the side issues [Pshat].

-A person does not have in the next world only what he brought into his mind in this world. Who ever knows the inside of Torah will enjoy the inner light. Who ever does not, will not get to enjoy it at all.

-The abomination occurring in our times, that most of the wise men of Yisroel have already strayed far from the truth and the sweet light, the glory of G-D our master. They go after calculations of nothingness. They lean after power and honor.

Quotes from Yarim Moshe (page 221)

-The Ari was very justified when he said the main occupation of a man should only be in the mysteries of the Torah.

-Who ever does not have a sharp mind should spend his day learning Kabbalah and not Pshat. This is the true way and it definitely pleases G-D. Even though this is not accepted by most rabbis, there is no way other then this.

-In the Zohar Shir Hasherim it says "Those who mastered only Pshat, after they die they are removed from all upper realms."